xref: /external/chromium_org/third_party/WebKit/Source/core/rendering/RenderBlockFlow.cpp

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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#include "config.h"
#include "core/rendering/RenderBlockFlow.h"

#include "core/accessibility/AXObjectCache.h"
#include "core/frame/FrameView.h"
#include "core/frame/LocalFrame.h"
#include "core/frame/Settings.h"
#include "core/html/HTMLDialogElement.h"
#include "core/paint/BlockFlowPainter.h"
#include "core/rendering/HitTestLocation.h"
#include "core/rendering/RenderFlowThread.h"
#include "core/rendering/RenderLayer.h"
#include "core/rendering/RenderMultiColumnFlowThread.h"
#include "core/rendering/RenderPagedFlowThread.h"
#include "core/rendering/RenderText.h"
#include "core/rendering/RenderView.h"
#include "core/rendering/TextAutosizer.h"
#include "core/rendering/line/LineWidth.h"
#include "core/rendering/svg/SVGTextRunRenderingContext.h"
#include "platform/text/BidiTextRun.h"

namespace blink {

bool RenderBlockFlow::s_canPropagateFloatIntoSibling = false;

struct SameSizeAsMarginInfo {
    uint16_t bitfields;
    LayoutUnit margins[2];
};

COMPILE_ASSERT(sizeof(RenderBlockFlow::MarginValues) == sizeof(LayoutUnit[4]), MarginValues_should_stay_small);

class MarginInfo {
    // Collapsing flags for whether we can collapse our margins with our children's margins.
    bool m_canCollapseWithChildren : 1;
    bool m_canCollapseMarginBeforeWithChildren : 1;
    bool m_canCollapseMarginAfterWithChildren : 1;
    bool m_canCollapseMarginAfterWithLastChild: 1;

    // Whether or not we are a quirky container, i.e., do we collapse away top and bottom
    // margins in our container. Table cells and the body are the common examples. We
    // also have a custom style property for Safari RSS to deal with TypePad blog articles.
    bool m_quirkContainer : 1;

    // This flag tracks whether we are still looking at child margins that can all collapse together at the beginning of a block.
    // They may or may not collapse with the top margin of the block (|m_canCollapseTopWithChildren| tells us that), but they will
    // always be collapsing with one another. This variable can remain set to true through multiple iterations
    // as long as we keep encountering self-collapsing blocks.
    bool m_atBeforeSideOfBlock : 1;

    // This flag is set when we know we're examining bottom margins and we know we're at the bottom of the block.
    bool m_atAfterSideOfBlock : 1;

    // These variables are used to detect quirky margins that we need to collapse away (in table cells
    // and in the body element).
    bool m_hasMarginBeforeQuirk : 1;
    bool m_hasMarginAfterQuirk : 1;
    bool m_determinedMarginBeforeQuirk : 1;

    bool m_discardMargin : 1;

    // These flags track the previous maximal positive and negative margins.
    LayoutUnit m_positiveMargin;
    LayoutUnit m_negativeMargin;

public:
    MarginInfo(RenderBlockFlow*, LayoutUnit beforeBorderPadding, LayoutUnit afterBorderPadding);

    void setAtBeforeSideOfBlock(bool b) { m_atBeforeSideOfBlock = b; }
    void setAtAfterSideOfBlock(bool b) { m_atAfterSideOfBlock = b; }
    void clearMargin()
    {
        m_positiveMargin = 0;
        m_negativeMargin = 0;
    }
    void setHasMarginBeforeQuirk(bool b) { m_hasMarginBeforeQuirk = b; }
    void setHasMarginAfterQuirk(bool b) { m_hasMarginAfterQuirk = b; }
    void setDeterminedMarginBeforeQuirk(bool b) { m_determinedMarginBeforeQuirk = b; }
    void setPositiveMargin(LayoutUnit p) { ASSERT(!m_discardMargin); m_positiveMargin = p; }
    void setNegativeMargin(LayoutUnit n) { ASSERT(!m_discardMargin); m_negativeMargin = n; }
    void setPositiveMarginIfLarger(LayoutUnit p)
    {
        ASSERT(!m_discardMargin);
        if (p > m_positiveMargin)
            m_positiveMargin = p;
    }
    void setNegativeMarginIfLarger(LayoutUnit n)
    {
        ASSERT(!m_discardMargin);
        if (n > m_negativeMargin)
            m_negativeMargin = n;
    }

    void setMargin(LayoutUnit p, LayoutUnit n) { ASSERT(!m_discardMargin); m_positiveMargin = p; m_negativeMargin = n; }
    void setCanCollapseMarginAfterWithChildren(bool collapse) { m_canCollapseMarginAfterWithChildren = collapse; }
    void setCanCollapseMarginAfterWithLastChild(bool collapse) { m_canCollapseMarginAfterWithLastChild = collapse; }
    void setDiscardMargin(bool value) { m_discardMargin = value; }

    bool atBeforeSideOfBlock() const { return m_atBeforeSideOfBlock; }
    bool canCollapseWithMarginBefore() const { return m_atBeforeSideOfBlock && m_canCollapseMarginBeforeWithChildren; }
    bool canCollapseWithMarginAfter() const { return m_atAfterSideOfBlock && m_canCollapseMarginAfterWithChildren; }
    bool canCollapseMarginBeforeWithChildren() const { return m_canCollapseMarginBeforeWithChildren; }
    bool canCollapseMarginAfterWithChildren() const { return m_canCollapseMarginAfterWithChildren; }
    bool canCollapseMarginAfterWithLastChild() const { return m_canCollapseMarginAfterWithLastChild; }
    bool quirkContainer() const { return m_quirkContainer; }
    bool determinedMarginBeforeQuirk() const { return m_determinedMarginBeforeQuirk; }
    bool hasMarginBeforeQuirk() const { return m_hasMarginBeforeQuirk; }
    bool hasMarginAfterQuirk() const { return m_hasMarginAfterQuirk; }
    LayoutUnit positiveMargin() const { return m_positiveMargin; }
    LayoutUnit negativeMargin() const { return m_negativeMargin; }
    bool discardMargin() const { return m_discardMargin; }
    LayoutUnit margin() const { return m_positiveMargin - m_negativeMargin; }
};
static bool inNormalFlow(RenderBox* child)
{
    RenderBlock* curr = child->containingBlock();
    RenderView* renderView = child->view();
    while (curr && curr != renderView) {
        if (curr->hasColumns() || curr->isRenderFlowThread())
            return true;
        if (curr->isFloatingOrOutOfFlowPositioned())
            return false;
        curr = curr->containingBlock();
    }
    return true;
}

void RenderBlockFlow::RenderBlockFlowRareData::trace(Visitor* visitor)
{
    visitor->trace(m_multiColumnFlowThread);
}

RenderBlockFlow::RenderBlockFlow(ContainerNode* node)
    : RenderBlock(node)
{
    COMPILE_ASSERT(sizeof(MarginInfo) == sizeof(SameSizeAsMarginInfo), MarginInfo_should_stay_small);
    setChildrenInline(true);
}

RenderBlockFlow::~RenderBlockFlow()
{
}

void RenderBlockFlow::trace(Visitor* visitor)
{
    visitor->trace(m_rareData);
    RenderBlock::trace(visitor);
}

RenderBlockFlow* RenderBlockFlow::createAnonymous(Document* document)
{
    RenderBlockFlow* renderer = new RenderBlockFlow(0);
    renderer->setDocumentForAnonymous(document);
    return renderer;
}

RenderObject* RenderBlockFlow::layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
{
    RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread();
    if (!flowThread)
        return 0;
    setLogicalTopForChild(flowThread, borderBefore() + paddingBefore());
    flowThread->layoutColumns(relayoutChildren, layoutScope);
    determineLogicalLeftPositionForChild(flowThread);
    return flowThread;
}

bool RenderBlockFlow::updateLogicalWidthAndColumnWidth()
{
    bool relayoutChildren = RenderBlock::updateLogicalWidthAndColumnWidth();
    if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
        if (flowThread->needsNewWidth())
            return true;
    }
    return relayoutChildren;
}

void RenderBlockFlow::checkForPaginationLogicalHeightChange(LayoutUnit& pageLogicalHeight, bool& pageLogicalHeightChanged, bool& hasSpecifiedPageLogicalHeight)
{
    if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
        LogicalExtentComputedValues computedValues;
        computeLogicalHeight(LayoutUnit(), logicalTop(), computedValues);
        LayoutUnit columnHeight = computedValues.m_extent - borderAndPaddingLogicalHeight() - scrollbarLogicalHeight();
        pageLogicalHeightChanged = columnHeight != flowThread->columnHeightAvailable();
        flowThread->setColumnHeightAvailable(std::max<LayoutUnit>(columnHeight, 0));
    } else if (hasColumns()) {
        ColumnInfo* colInfo = columnInfo();

        if (!pageLogicalHeight) {
            LayoutUnit oldLogicalHeight = logicalHeight();
            setLogicalHeight(0);
            // We need to go ahead and set our explicit page height if one exists, so that we can
            // avoid doing two layout passes.
            updateLogicalHeight();
            LayoutUnit columnHeight = contentLogicalHeight();
            if (columnHeight > 0) {
                pageLogicalHeight = columnHeight;
                hasSpecifiedPageLogicalHeight = true;
            }
            setLogicalHeight(oldLogicalHeight);
        }
        if (colInfo->columnHeight() != pageLogicalHeight && everHadLayout()) {
            colInfo->setColumnHeight(pageLogicalHeight);
            pageLogicalHeightChanged = true;
        }

        if (!hasSpecifiedPageLogicalHeight && !pageLogicalHeight)
            colInfo->clearForcedBreaks();
    } else if (isRenderFlowThread()) {
        RenderFlowThread* flowThread = toRenderFlowThread(this);

        // FIXME: This is a hack to always make sure we have a page logical height, if said height
        // is known. The page logical height thing in LayoutState is meaningless for flow
        // thread-based pagination (page height isn't necessarily uniform throughout the flow
        // thread), but as long as it is used universally as a means to determine whether page
        // height is known or not, we need this. Page height is unknown when column balancing is
        // enabled and flow thread height is still unknown (i.e. during the first layout pass). When
        // it's unknown, we need to prevent the pagination code from assuming page breaks everywhere
        // and thereby eating every top margin. It should be trivial to clean up and get rid of this
        // hack once the old multicol implementation is gone.
        pageLogicalHeight = flowThread->isPageLogicalHeightKnown() ? LayoutUnit(1) : LayoutUnit(0);

        pageLogicalHeightChanged = flowThread->pageLogicalSizeChanged();
    }
}

bool RenderBlockFlow::shouldRelayoutForPagination(LayoutUnit& pageLogicalHeight, LayoutUnit layoutOverflowLogicalBottom) const
{
    // FIXME: We don't balance properly at all in the presence of forced page breaks. We need to understand what
    // the distance between forced page breaks is so that we can avoid making the minimum column height too tall.
    ColumnInfo* colInfo = columnInfo();
    LayoutUnit columnHeight = pageLogicalHeight;
    const int minColumnCount = colInfo->forcedBreaks() + 1;
    const int desiredColumnCount = colInfo->desiredColumnCount();
    if (minColumnCount >= desiredColumnCount) {
        // The forced page breaks are in control of the balancing. Just set the column height to the
        // maximum page break distance.
        if (!pageLogicalHeight) {
            LayoutUnit distanceBetweenBreaks = std::max<LayoutUnit>(colInfo->maximumDistanceBetweenForcedBreaks(),
                view()->layoutState()->pageLogicalOffset(*this, borderBefore() + paddingBefore() + layoutOverflowLogicalBottom) - colInfo->forcedBreakOffset());
            columnHeight = std::max(colInfo->minimumColumnHeight(), distanceBetweenBreaks);
        }
    } else if (layoutOverflowLogicalBottom > boundedMultiply(pageLogicalHeight, desiredColumnCount)) {
        // Now that we know the intrinsic height of the columns, we have to rebalance them.
        columnHeight = std::max<LayoutUnit>(colInfo->minimumColumnHeight(), ceilf(layoutOverflowLogicalBottom.toFloat() / desiredColumnCount));
    }

    if (columnHeight && columnHeight != pageLogicalHeight) {
        pageLogicalHeight = columnHeight;
        return true;
    }

    return false;
}

void RenderBlockFlow::setColumnCountAndHeight(unsigned count, LayoutUnit pageLogicalHeight)
{
    ColumnInfo* colInfo = columnInfo();
    if (pageLogicalHeight)
        colInfo->setColumnCountAndHeight(count, pageLogicalHeight);

    if (columnCount(colInfo)) {
        setLogicalHeight(borderBefore() + paddingBefore() + colInfo->columnHeight() + borderAfter() + paddingAfter() + scrollbarLogicalHeight());
        m_overflow.clear();
    }
}

void RenderBlockFlow::setBreakAtLineToAvoidWidow(int lineToBreak)
{
    ASSERT(lineToBreak >= 0);
    ensureRareData();
    ASSERT(!m_rareData->m_didBreakAtLineToAvoidWidow);
    m_rareData->m_lineBreakToAvoidWidow = lineToBreak;
}

void RenderBlockFlow::setDidBreakAtLineToAvoidWidow()
{
    ASSERT(!shouldBreakAtLineToAvoidWidow());

    // This function should be called only after a break was applied to avoid widows
    // so assert |m_rareData| exists.
    ASSERT(m_rareData);

    m_rareData->m_didBreakAtLineToAvoidWidow = true;
}

void RenderBlockFlow::clearDidBreakAtLineToAvoidWidow()
{
    if (!m_rareData)
        return;

    m_rareData->m_didBreakAtLineToAvoidWidow = false;
}

void RenderBlockFlow::clearShouldBreakAtLineToAvoidWidow() const
{
    ASSERT(shouldBreakAtLineToAvoidWidow());
    if (!m_rareData)
        return;

    m_rareData->m_lineBreakToAvoidWidow = -1;
}

bool RenderBlockFlow::isSelfCollapsingBlock() const
{
    m_hasOnlySelfCollapsingChildren = RenderBlock::isSelfCollapsingBlock();
    return m_hasOnlySelfCollapsingChildren;
}

void RenderBlockFlow::layoutBlock(bool relayoutChildren)
{
    ASSERT(needsLayout());
    ASSERT(isInlineBlockOrInlineTable() || !isInline());

    // If we are self-collapsing with self-collapsing descendants this will get set to save us burrowing through our
    // descendants every time in |isSelfCollapsingBlock|. We reset it here so that |isSelfCollapsingBlock| attempts to burrow
    // at least once and so that it always gives a reliable result reflecting the latest layout.
    m_hasOnlySelfCollapsingChildren = false;

    if (!relayoutChildren && simplifiedLayout())
        return;

    SubtreeLayoutScope layoutScope(*this);

    // Multiple passes might be required for column and pagination based layout
    // In the case of the old column code the number of passes will only be two
    // however, in the newer column code the number of passes could equal the
    // number of columns.
    bool done = false;
    LayoutUnit pageLogicalHeight = 0;
    while (!done)
        done = layoutBlockFlow(relayoutChildren, pageLogicalHeight, layoutScope);

    fitBorderToLinesIfNeeded();

    RenderView* renderView = view();
    if (renderView->layoutState()->pageLogicalHeight())
        setPageLogicalOffset(renderView->layoutState()->pageLogicalOffset(*this, logicalTop()));

    updateLayerTransformAfterLayout();

    // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
    // we overflow or not.
    updateScrollInfoAfterLayout();

    if (m_paintInvalidationLogicalTop != m_paintInvalidationLogicalBottom) {
        bool hasVisibleContent = style()->visibility() == VISIBLE;
        if (!hasVisibleContent) {
            RenderLayer* layer = enclosingLayer();
            layer->updateDescendantDependentFlags();
            hasVisibleContent = layer->hasVisibleContent();
        }
        if (hasVisibleContent)
            setShouldInvalidateOverflowForPaint(true);
    }

    if (isHTMLDialogElement(node()) && isOutOfFlowPositioned())
        positionDialog();

    clearNeedsLayout();
}

inline bool RenderBlockFlow::layoutBlockFlow(bool relayoutChildren, LayoutUnit &pageLogicalHeight, SubtreeLayoutScope& layoutScope)
{
    LayoutUnit oldLeft = logicalLeft();
    bool logicalWidthChanged = updateLogicalWidthAndColumnWidth();
    relayoutChildren |= logicalWidthChanged;

    rebuildFloatsFromIntruding();

    bool pageLogicalHeightChanged = false;
    bool hasSpecifiedPageLogicalHeight = false;
    checkForPaginationLogicalHeightChange(pageLogicalHeight, pageLogicalHeightChanged, hasSpecifiedPageLogicalHeight);
    if (pageLogicalHeightChanged)
        relayoutChildren = true;

    LayoutState state(*this, locationOffset(), pageLogicalHeight, pageLogicalHeightChanged, columnInfo(), logicalWidthChanged);

    // We use four values, maxTopPos, maxTopNeg, maxBottomPos, and maxBottomNeg, to track
    // our current maximal positive and negative margins. These values are used when we
    // are collapsed with adjacent blocks, so for example, if you have block A and B
    // collapsing together, then you'd take the maximal positive margin from both A and B
    // and subtract it from the maximal negative margin from both A and B to get the
    // true collapsed margin. This algorithm is recursive, so when we finish layout()
    // our block knows its current maximal positive/negative values.
    //
    // Start out by setting our margin values to our current margins. Table cells have
    // no margins, so we don't fill in the values for table cells.
    if (!isTableCell()) {
        initMaxMarginValues();
        setHasMarginBeforeQuirk(style()->hasMarginBeforeQuirk());
        setHasMarginAfterQuirk(style()->hasMarginAfterQuirk());
        setPaginationStrut(0);
    }

    LayoutUnit beforeEdge = borderBefore() + paddingBefore();
    LayoutUnit afterEdge = borderAfter() + paddingAfter() + scrollbarLogicalHeight();
    LayoutUnit previousHeight = logicalHeight();
    setLogicalHeight(beforeEdge);

    m_paintInvalidationLogicalTop = 0;
    m_paintInvalidationLogicalBottom = 0;
    if (!firstChild() && !isAnonymousBlock())
        setChildrenInline(true);

    TextAutosizer::LayoutScope textAutosizerLayoutScope(this);

    if (childrenInline())
        layoutInlineChildren(relayoutChildren, m_paintInvalidationLogicalTop, m_paintInvalidationLogicalBottom, afterEdge);
    else
        layoutBlockChildren(relayoutChildren, layoutScope, beforeEdge, afterEdge);

    // Expand our intrinsic height to encompass floats.
    if (lowestFloatLogicalBottom() > (logicalHeight() - afterEdge) && createsBlockFormattingContext())
        setLogicalHeight(lowestFloatLogicalBottom() + afterEdge);

    if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
        if (flowThread->recalculateColumnHeights()) {
            setChildNeedsLayout(MarkOnlyThis);
            return false;
        }
    } else if (hasColumns()) {
        OwnPtr<RenderOverflow> savedOverflow = m_overflow.release();
        if (childrenInline())
            addOverflowFromInlineChildren();
        else
            addOverflowFromBlockChildren();
        LayoutUnit layoutOverflowLogicalBottom = (isHorizontalWritingMode() ? layoutOverflowRect().maxY() : layoutOverflowRect().maxX()) - borderBefore() - paddingBefore();
        m_overflow = savedOverflow.release();

        if (!hasSpecifiedPageLogicalHeight && shouldRelayoutForPagination(pageLogicalHeight, layoutOverflowLogicalBottom)) {
            setEverHadLayout(true);
            return false;
        }

        setColumnCountAndHeight(ceilf(layoutOverflowLogicalBottom.toFloat() / pageLogicalHeight.toFloat()), pageLogicalHeight.toFloat());
    }

    if (shouldBreakAtLineToAvoidWidow()) {
        setEverHadLayout(true);
        return false;
    }

    // Calculate our new height.
    LayoutUnit oldHeight = logicalHeight();
    LayoutUnit oldClientAfterEdge = clientLogicalBottom();

    updateLogicalHeight();
    LayoutUnit newHeight = logicalHeight();
    if (oldHeight > newHeight && !childrenInline()) {
        // One of our children's floats may have become an overhanging float for us.
        for (RenderObject* child = lastChild(); child; child = child->previousSibling()) {
            if (child->isRenderBlockFlow() && !child->isFloatingOrOutOfFlowPositioned()) {
                RenderBlockFlow* block = toRenderBlockFlow(child);
                if (block->lowestFloatLogicalBottom() + block->logicalTop() <= newHeight)
                    break;
                addOverhangingFloats(block, false);
            }
        }
    }

    bool heightChanged = (previousHeight != newHeight);
    if (heightChanged)
        relayoutChildren = true;

    layoutPositionedObjects(relayoutChildren || isDocumentElement(), oldLeft != logicalLeft() ? ForcedLayoutAfterContainingBlockMoved : DefaultLayout);

    // Add overflow from children (unless we're multi-column, since in that case all our child overflow is clipped anyway).
    computeOverflow(oldClientAfterEdge);

    m_descendantsWithFloatsMarkedForLayout = false;
    return true;
}

void RenderBlockFlow::determineLogicalLeftPositionForChild(RenderBox* child)
{
    LayoutUnit startPosition = borderStart() + paddingStart();
    LayoutUnit initialStartPosition = startPosition;
    if (style()->shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
        startPosition -= verticalScrollbarWidth();
    LayoutUnit totalAvailableLogicalWidth = borderAndPaddingLogicalWidth() + availableLogicalWidth();

    LayoutUnit childMarginStart = marginStartForChild(child);
    LayoutUnit newPosition = startPosition + childMarginStart;

    LayoutUnit positionToAvoidFloats;
    if (child->avoidsFloats() && containsFloats() && !flowThreadContainingBlock())
        positionToAvoidFloats = startOffsetForLine(logicalTopForChild(child), false, logicalHeightForChild(child));

    // If the child has an offset from the content edge to avoid floats then use that, otherwise let any negative
    // margin pull it back over the content edge or any positive margin push it out.
    // If the child is being centred then the margin calculated to do that has factored in any offset required to
    // avoid floats, so use it if necessary.
    if (style()->textAlign() == WEBKIT_CENTER || child->style()->marginStartUsing(style()).isAuto())
        newPosition = std::max(newPosition, positionToAvoidFloats + childMarginStart);
    else if (positionToAvoidFloats > initialStartPosition)
        newPosition = std::max(newPosition, positionToAvoidFloats);

    setLogicalLeftForChild(child, style()->isLeftToRightDirection() ? newPosition : totalAvailableLogicalWidth - newPosition - logicalWidthForChild(child));
}

void RenderBlockFlow::setLogicalLeftForChild(RenderBox* child, LayoutUnit logicalLeft)
{
    if (isHorizontalWritingMode()) {
        child->setX(logicalLeft);
    } else {
        child->setY(logicalLeft);
    }
}

void RenderBlockFlow::setLogicalTopForChild(RenderBox* child, LayoutUnit logicalTop)
{
    if (isHorizontalWritingMode()) {
        child->setY(logicalTop);
    } else {
        child->setX(logicalTop);
    }
}

void RenderBlockFlow::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo, LayoutUnit& previousFloatLogicalBottom)
{
    LayoutUnit oldPosMarginBefore = maxPositiveMarginBefore();
    LayoutUnit oldNegMarginBefore = maxNegativeMarginBefore();

    // The child is a normal flow object. Compute the margins we will use for collapsing now.
    child->computeAndSetBlockDirectionMargins(this);

    // Try to guess our correct logical top position. In most cases this guess will
    // be correct. Only if we're wrong (when we compute the real logical top position)
    // will we have to potentially relayout.
    LayoutUnit estimateWithoutPagination;
    LayoutUnit logicalTopEstimate = estimateLogicalTopPosition(child, marginInfo, estimateWithoutPagination);

    // Cache our old rect so that we can dirty the proper paint invalidation rects if the child moves.
    LayoutRect oldRect = child->frameRect();
    LayoutUnit oldLogicalTop = logicalTopForChild(child);

    // Go ahead and position the child as though it didn't collapse with the top.
    setLogicalTopForChild(child, logicalTopEstimate);

    RenderBlockFlow* childRenderBlockFlow = child->isRenderBlockFlow() ? toRenderBlockFlow(child) : 0;
    bool markDescendantsWithFloats = false;
    if (logicalTopEstimate != oldLogicalTop && childRenderBlockFlow && !childRenderBlockFlow->avoidsFloats() && childRenderBlockFlow->containsFloats()) {
        markDescendantsWithFloats = true;
    } else if (UNLIKELY(logicalTopEstimate.mightBeSaturated())) {
        // logicalTopEstimate, returned by estimateLogicalTopPosition, might be saturated for
        // very large elements. If it does the comparison with oldLogicalTop might yield a
        // false negative as adding and removing margins, borders etc from a saturated number
        // might yield incorrect results. If this is the case always mark for layout.
        markDescendantsWithFloats = true;
    } else if (!child->avoidsFloats() || child->shrinkToAvoidFloats()) {
        // If an element might be affected by the presence of floats, then always mark it for
        // layout.
        LayoutUnit fb = std::max(previousFloatLogicalBottom, lowestFloatLogicalBottom());
        if (fb > logicalTopEstimate)
            markDescendantsWithFloats = true;
    }

    if (childRenderBlockFlow) {
        if (markDescendantsWithFloats)
            childRenderBlockFlow->markAllDescendantsWithFloatsForLayout();
        if (!child->isWritingModeRoot())
            previousFloatLogicalBottom = std::max(previousFloatLogicalBottom, oldLogicalTop + childRenderBlockFlow->lowestFloatLogicalBottom());
    }

    SubtreeLayoutScope layoutScope(*child);
    if (!child->needsLayout())
        child->markForPaginationRelayoutIfNeeded(layoutScope);

    bool childHadLayout = child->everHadLayout();
    bool childNeededLayout = child->needsLayout();
    if (childNeededLayout)
        child->layout();

    // Cache if we are at the top of the block right now.
    bool atBeforeSideOfBlock = marginInfo.atBeforeSideOfBlock();
    bool childIsSelfCollapsing = child->isSelfCollapsingBlock();

    // Now determine the correct ypos based off examination of collapsing margin
    // values.
    LayoutUnit logicalTopBeforeClear = collapseMargins(child, marginInfo, childIsSelfCollapsing);

    // Now check for clear.
    LayoutUnit logicalTopAfterClear = clearFloatsIfNeeded(child, marginInfo, oldPosMarginBefore, oldNegMarginBefore, logicalTopBeforeClear, childIsSelfCollapsing);

    bool paginated = view()->layoutState()->isPaginated();
    if (paginated) {
        logicalTopAfterClear = adjustBlockChildForPagination(logicalTopAfterClear, estimateWithoutPagination, child,
            atBeforeSideOfBlock && logicalTopBeforeClear == logicalTopAfterClear);
    }

    setLogicalTopForChild(child, logicalTopAfterClear);

    // Now we have a final top position. See if it really does end up being different from our estimate.
    // clearFloatsIfNeeded can also mark the child as needing a layout even though we didn't move. This happens
    // when collapseMargins dynamically adds overhanging floats because of a child with negative margins.
    if (logicalTopAfterClear != logicalTopEstimate || child->needsLayout() || (paginated && childRenderBlockFlow && childRenderBlockFlow->shouldBreakAtLineToAvoidWidow())) {
        SubtreeLayoutScope layoutScope(*child);
        if (child->shrinkToAvoidFloats()) {
            // The child's width depends on the line width.
            // When the child shifts to clear an item, its width can
            // change (because it has more available line width).
            // So go ahead and mark the item as dirty.
            layoutScope.setChildNeedsLayout(child);
        }

        if (childRenderBlockFlow && !childRenderBlockFlow->avoidsFloats() && childRenderBlockFlow->containsFloats())
            childRenderBlockFlow->markAllDescendantsWithFloatsForLayout();

        if (!child->needsLayout())
            child->markForPaginationRelayoutIfNeeded(layoutScope);

        // Our guess was wrong. Make the child lay itself out again.
        child->layoutIfNeeded();
    }

    // If we previously encountered a self-collapsing sibling of this child that had clearance then
    // we set this bit to ensure we would not collapse the child's margins, and those of any subsequent
    // self-collapsing siblings, with our parent. If this child is not self-collapsing then it can
    // collapse its margins with the parent so reset the bit.
    if (!marginInfo.canCollapseMarginAfterWithLastChild() && !childIsSelfCollapsing)
        marginInfo.setCanCollapseMarginAfterWithLastChild(true);

    // We are no longer at the top of the block if we encounter a non-empty child.
    // This has to be done after checking for clear, so that margins can be reset if a clear occurred.
    if (marginInfo.atBeforeSideOfBlock() && !childIsSelfCollapsing)
        marginInfo.setAtBeforeSideOfBlock(false);

    // Now place the child in the correct left position
    determineLogicalLeftPositionForChild(child);

    LayoutSize childOffset = child->location() - oldRect.location();

    // Update our height now that the child has been placed in the correct position.
    setLogicalHeight(logicalHeight() + logicalHeightForChild(child));
    if (mustSeparateMarginAfterForChild(child)) {
        setLogicalHeight(logicalHeight() + marginAfterForChild(child));
        marginInfo.clearMargin();
    }
    // If the child has overhanging floats that intrude into following siblings (or possibly out
    // of this block), then the parent gets notified of the floats now.
    if (childRenderBlockFlow)
        addOverhangingFloats(childRenderBlockFlow, !childNeededLayout);

    // If the child moved, we have to invalidate it's paint  as well as any floating/positioned
    // descendants. An exception is if we need a layout. In this case, we know we're going to
    // invalidate our paint (and the child) anyway.
    bool didNotDoFullLayoutAndMoved = childHadLayout && !selfNeedsLayout() && (childOffset.width() || childOffset.height());
    bool didNotLayoutAndNeedsPaintInvalidation = !childHadLayout && child->checkForPaintInvalidation();

    if (didNotDoFullLayoutAndMoved || didNotLayoutAndNeedsPaintInvalidation)
        child->invalidatePaintForOverhangingFloats(true);

    if (paginated) {
        // Check for an after page/column break.
        LayoutUnit newHeight = applyAfterBreak(child, logicalHeight(), marginInfo);
        if (newHeight != height())
            setLogicalHeight(newHeight);
    }
}

LayoutUnit RenderBlockFlow::adjustBlockChildForPagination(LayoutUnit logicalTopAfterClear, LayoutUnit estimateWithoutPagination, RenderBox* child, bool atBeforeSideOfBlock)
{
    RenderBlockFlow* childBlockFlow = child->isRenderBlockFlow() ? toRenderBlockFlow(child) : 0;

    if (estimateWithoutPagination != logicalTopAfterClear) {
        // Our guess prior to pagination movement was wrong. Before we attempt to paginate, let's try again at the new
        // position.
        setLogicalHeight(logicalTopAfterClear);
        setLogicalTopForChild(child, logicalTopAfterClear);

        if (child->shrinkToAvoidFloats()) {
            // The child's width depends on the line width.
            // When the child shifts to clear an item, its width can
            // change (because it has more available line width).
            // So go ahead and mark the item as dirty.
            child->setChildNeedsLayout(MarkOnlyThis);
        }

        SubtreeLayoutScope layoutScope(*child);

        if (childBlockFlow) {
            if (!childBlockFlow->avoidsFloats() && childBlockFlow->containsFloats())
                childBlockFlow->markAllDescendantsWithFloatsForLayout();
            if (!child->needsLayout())
                child->markForPaginationRelayoutIfNeeded(layoutScope);
        }

        // Our guess was wrong. Make the child lay itself out again.
        child->layoutIfNeeded();
    }

    LayoutUnit oldTop = logicalTopAfterClear;

    // If the object has a page or column break value of "before", then we should shift to the top of the next page.
    LayoutUnit result = applyBeforeBreak(child, logicalTopAfterClear);

    // For replaced elements and scrolled elements, we want to shift them to the next page if they don't fit on the current one.
    LayoutUnit logicalTopBeforeUnsplittableAdjustment = result;
    LayoutUnit logicalTopAfterUnsplittableAdjustment = adjustForUnsplittableChild(child, result);

    LayoutUnit paginationStrut = 0;
    LayoutUnit unsplittableAdjustmentDelta = logicalTopAfterUnsplittableAdjustment - logicalTopBeforeUnsplittableAdjustment;
    LayoutUnit childLogicalHeight = child->logicalHeight();
    if (unsplittableAdjustmentDelta) {
        setPageBreak(result, childLogicalHeight - unsplittableAdjustmentDelta);
        paginationStrut = unsplittableAdjustmentDelta;
    } else if (childBlockFlow && childBlockFlow->paginationStrut()) {
        paginationStrut = childBlockFlow->paginationStrut();
    }

    if (paginationStrut) {
        // We are willing to propagate out to our parent block as long as we were at the top of the block prior
        // to collapsing our margins, and as long as we didn't clear or move as a result of other pagination.
        if (atBeforeSideOfBlock && oldTop == result && !isOutOfFlowPositioned() && !isTableCell()) {
            // FIXME: Should really check if we're exceeding the page height before propagating the strut, but we don't
            // have all the information to do so (the strut only has the remaining amount to push). Gecko gets this wrong too
            // and pushes to the next page anyway, so not too concerned about it.
            setPaginationStrut(result + paginationStrut);
            if (childBlockFlow)
                childBlockFlow->setPaginationStrut(0);
        } else {
            result += paginationStrut;
        }
    }

    if (!unsplittableAdjustmentDelta) {
        if (LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(result)) {
            LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(result, ExcludePageBoundary);
            LayoutUnit spaceShortage = childLogicalHeight - remainingLogicalHeight;
            if (spaceShortage > 0) {
                // If the child crosses a column boundary, report a break, in case nothing inside it
                // has already done so. The column balancer needs to know how much it has to stretch
                // the columns to make more content fit. If no breaks are reported (but do occur),
                // the balancer will have no clue. Only measure the space after the last column
                // boundary, in case it crosses more than one.
                LayoutUnit spaceShortageInLastColumn = intMod(spaceShortage, pageLogicalHeight);
                setPageBreak(result, spaceShortageInLastColumn ? spaceShortageInLastColumn : spaceShortage);
            } else if (remainingLogicalHeight == pageLogicalHeight && offsetFromLogicalTopOfFirstPage() + child->logicalTop()) {
                // We're at the very top of a page or column, and it's not the first one. This child
                // may turn out to be the smallest piece of content that causes a page break, so we
                // need to report it.
                setPageBreak(result, childLogicalHeight);
            }
        }
    }

    // Similar to how we apply clearance. Go ahead and boost height() to be the place where we're going to position the child.
    setLogicalHeight(logicalHeight() + (result - oldTop));

    // Return the final adjusted logical top.
    return result;
}

static inline LayoutUnit calculateMinimumPageHeight(RenderStyle* renderStyle, RootInlineBox* lastLine, LayoutUnit lineTop, LayoutUnit lineBottom)
{
    // We may require a certain minimum number of lines per page in order to satisfy
    // orphans and widows, and that may affect the minimum page height.
    unsigned lineCount = std::max<unsigned>(renderStyle->hasAutoOrphans() ? 1 : renderStyle->orphans(), renderStyle->hasAutoWidows() ? 1 : renderStyle->widows());
    if (lineCount > 1) {
        RootInlineBox* line = lastLine;
        for (unsigned i = 1; i < lineCount && line->prevRootBox(); i++)
            line = line->prevRootBox();

        // FIXME: Paginating using line overflow isn't all fine. See FIXME in
        // adjustLinePositionForPagination() for more details.
        LayoutRect overflow = line->logicalVisualOverflowRect(line->lineTop(), line->lineBottom());
        lineTop = std::min(line->lineTopWithLeading(), overflow.y());
    }
    return lineBottom - lineTop;
}

void RenderBlockFlow::adjustLinePositionForPagination(RootInlineBox* lineBox, LayoutUnit& delta, RenderFlowThread* flowThread)
{
    // FIXME: For now we paginate using line overflow. This ensures that lines don't overlap at all when we
    // put a strut between them for pagination purposes. However, this really isn't the desired rendering, since
    // the line on the top of the next page will appear too far down relative to the same kind of line at the top
    // of the first column.
    //
    // The rendering we would like to see is one where the lineTopWithLeading is at the top of the column, and any line overflow
    // simply spills out above the top of the column. This effect would match what happens at the top of the first column.
    // We can't achieve this rendering, however, until we stop columns from clipping to the column bounds (thus allowing
    // for overflow to occur), and then cache visible overflow for each column rect.
    //
    // Furthermore, the paint we have to do when a column has overflow has to be special. We need to exclude
    // content that paints in a previous column (and content that paints in the following column).
    //
    // For now we'll at least honor the lineTopWithLeading when paginating if it is above the logical top overflow. This will
    // at least make positive leading work in typical cases.
    //
    // FIXME: Another problem with simply moving lines is that the available line width may change (because of floats).
    // Technically if the location we move the line to has a different line width than our old position, then we need to dirty the
    // line and all following lines.
    LayoutRect logicalVisualOverflow = lineBox->logicalVisualOverflowRect(lineBox->lineTop(), lineBox->lineBottom());
    LayoutUnit logicalOffset = std::min(lineBox->lineTopWithLeading(), logicalVisualOverflow.y());
    LayoutUnit logicalBottom = std::max(lineBox->lineBottomWithLeading(), logicalVisualOverflow.maxY());
    LayoutUnit lineHeight = logicalBottom - logicalOffset;
    updateMinimumPageHeight(logicalOffset, calculateMinimumPageHeight(style(), lineBox, logicalOffset, logicalBottom));
    logicalOffset += delta;
    lineBox->setPaginationStrut(0);
    lineBox->setIsFirstAfterPageBreak(false);
    LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
    bool hasUniformPageLogicalHeight = !flowThread || flowThread->regionsHaveUniformLogicalHeight();
    // If lineHeight is greater than pageLogicalHeight, but logicalVisualOverflow.height() still fits, we are
    // still going to add a strut, so that the visible overflow fits on a single page.
    if (!pageLogicalHeight || (hasUniformPageLogicalHeight && logicalVisualOverflow.height() > pageLogicalHeight)) {
        // FIXME: In case the line aligns with the top of the page (or it's slightly shifted downwards) it will not be marked as the first line in the page.
        // From here, the fix is not straightforward because it's not easy to always determine when the current line is the first in the page.
        return;
    }
    LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);

    int lineIndex = lineCount(lineBox);
    if (remainingLogicalHeight < lineHeight || (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex)) {
        if (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex) {
            clearShouldBreakAtLineToAvoidWidow();
            setDidBreakAtLineToAvoidWidow();
        }
        if (lineHeight > pageLogicalHeight) {
            // Split the top margin in order to avoid splitting the visible part of the line.
            remainingLogicalHeight -= std::min(lineHeight - pageLogicalHeight, std::max<LayoutUnit>(0, logicalVisualOverflow.y() - lineBox->lineTopWithLeading()));
        }
        LayoutUnit totalLogicalHeight = lineHeight + std::max<LayoutUnit>(0, logicalOffset);
        LayoutUnit pageLogicalHeightAtNewOffset = hasUniformPageLogicalHeight ? pageLogicalHeight : pageLogicalHeightForOffset(logicalOffset + remainingLogicalHeight);
        setPageBreak(logicalOffset, lineHeight - remainingLogicalHeight);
        if (((lineBox == firstRootBox() && totalLogicalHeight < pageLogicalHeightAtNewOffset) || (!style()->hasAutoOrphans() && style()->orphans() >= lineIndex))
            && !isOutOfFlowPositioned() && !isTableCell()) {
            setPaginationStrut(remainingLogicalHeight + std::max<LayoutUnit>(0, logicalOffset));
        } else {
            delta += remainingLogicalHeight;
            lineBox->setPaginationStrut(remainingLogicalHeight);
            lineBox->setIsFirstAfterPageBreak(true);
        }
    } else if (remainingLogicalHeight == pageLogicalHeight) {
        // We're at the very top of a page or column.
        if (lineBox != firstRootBox())
            lineBox->setIsFirstAfterPageBreak(true);
        if (lineBox != firstRootBox() || offsetFromLogicalTopOfFirstPage())
            setPageBreak(logicalOffset, lineHeight);
    }
}

LayoutUnit RenderBlockFlow::adjustForUnsplittableChild(RenderBox* child, LayoutUnit logicalOffset, bool includeMargins)
{
    bool checkColumnBreaks = view()->layoutState()->isPaginatingColumns() || flowThreadContainingBlock();
    bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight();
    bool isUnsplittable = child->isUnsplittableForPagination() || (checkColumnBreaks && child->style()->columnBreakInside() == PBAVOID)
        || (checkPageBreaks && child->style()->pageBreakInside() == PBAVOID);
    if (!isUnsplittable)
        return logicalOffset;
    LayoutUnit childLogicalHeight = logicalHeightForChild(child) + (includeMargins ? marginBeforeForChild(child) + marginAfterForChild(child) : LayoutUnit());
    LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
    updateMinimumPageHeight(logicalOffset, childLogicalHeight);
    if (!pageLogicalHeight || childLogicalHeight > pageLogicalHeight)
        return logicalOffset;
    LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);
    if (remainingLogicalHeight < childLogicalHeight)
        return logicalOffset + remainingLogicalHeight;
    return logicalOffset;
}

void RenderBlockFlow::rebuildFloatsFromIntruding()
{
    if (m_floatingObjects)
        m_floatingObjects->setHorizontalWritingMode(isHorizontalWritingMode());

    HashSet<RenderBox*> oldIntrudingFloatSet;
    if (!childrenInline() && m_floatingObjects) {
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator end = floatingObjectSet.end();
        for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
            FloatingObject* floatingObject = it->get();
            if (!floatingObject->isDescendant())
                oldIntrudingFloatSet.add(floatingObject->renderer());
        }
    }

    // Inline blocks are covered by the isReplaced() check in the avoidFloats method.
    if (avoidsFloats() || isDocumentElement() || isRenderView() || isFloatingOrOutOfFlowPositioned() || isTableCell()) {
        if (m_floatingObjects) {
            m_floatingObjects->clear();
        }
        if (!oldIntrudingFloatSet.isEmpty())
            markAllDescendantsWithFloatsForLayout();
        return;
    }

    RendererToFloatInfoMap floatMap;

    if (m_floatingObjects) {
        if (childrenInline())
            m_floatingObjects->moveAllToFloatInfoMap(floatMap);
        else
            m_floatingObjects->clear();
    }

    // We should not process floats if the parent node is not a RenderBlockFlow. Otherwise, we will add
    // floats in an invalid context. This will cause a crash arising from a bad cast on the parent.
    // See <rdar://problem/8049753>, where float property is applied on a text node in a SVG.
    if (!parent() || !parent()->isRenderBlockFlow())
        return;

    // Attempt to locate a previous sibling with overhanging floats. We skip any elements that
    // may have shifted to avoid floats, and any objects whose floats cannot interact with objects
    // outside it (i.e. objects that create a new block formatting context).
    RenderBlockFlow* parentBlockFlow = toRenderBlockFlow(parent());
    bool parentHasFloats = false;
    RenderObject* prev = previousSibling();
    while (prev && (!prev->isBox() || !prev->isRenderBlock() || toRenderBlock(prev)->avoidsFloats() || toRenderBlock(prev)->createsBlockFormattingContext())) {
        if (prev->isFloating())
            parentHasFloats = true;
        prev = prev->previousSibling();
    }

    // First add in floats from the parent. Self-collapsing blocks let their parent track any floats that intrude into
    // them (as opposed to floats they contain themselves) so check for those here too.
    LayoutUnit logicalTopOffset = logicalTop();
    bool parentHasIntrudingFloats = !parentHasFloats && (!prev || toRenderBlockFlow(prev)->isSelfCollapsingBlock()) && parentBlockFlow->lowestFloatLogicalBottom() > logicalTopOffset;
    if (parentHasFloats || parentHasIntrudingFloats)
        addIntrudingFloats(parentBlockFlow, parentBlockFlow->logicalLeftOffsetForContent(), logicalTopOffset);

    // Add overhanging floats from the previous RenderBlockFlow, but only if it has a float that intrudes into our space.
    if (prev) {
        RenderBlockFlow* blockFlow = toRenderBlockFlow(prev);
        logicalTopOffset -= blockFlow->logicalTop();
        if (blockFlow->lowestFloatLogicalBottom() > logicalTopOffset)
            addIntrudingFloats(blockFlow, 0, logicalTopOffset);
    }

    if (childrenInline()) {
        LayoutUnit changeLogicalTop = LayoutUnit::max();
        LayoutUnit changeLogicalBottom = LayoutUnit::min();
        if (m_floatingObjects) {
            const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
            FloatingObjectSetIterator end = floatingObjectSet.end();
            for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
                FloatingObject* floatingObject = it->get();
                FloatingObject* oldFloatingObject = floatMap.get(floatingObject->renderer());
                LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);
                if (oldFloatingObject) {
                    LayoutUnit oldLogicalBottom = logicalBottomForFloat(oldFloatingObject);
                    if (logicalWidthForFloat(floatingObject) != logicalWidthForFloat(oldFloatingObject) || logicalLeftForFloat(floatingObject) != logicalLeftForFloat(oldFloatingObject)) {
                        changeLogicalTop = 0;
                        changeLogicalBottom = std::max(changeLogicalBottom, std::max(logicalBottom, oldLogicalBottom));
                    } else {
                        if (logicalBottom != oldLogicalBottom) {
                            changeLogicalTop = std::min(changeLogicalTop, std::min(logicalBottom, oldLogicalBottom));
                            changeLogicalBottom = std::max(changeLogicalBottom, std::max(logicalBottom, oldLogicalBottom));
                        }
                        LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
                        LayoutUnit oldLogicalTop = logicalTopForFloat(oldFloatingObject);
                        if (logicalTop != oldLogicalTop) {
                            changeLogicalTop = std::min(changeLogicalTop, std::min(logicalTop, oldLogicalTop));
                            changeLogicalBottom = std::max(changeLogicalBottom, std::max(logicalTop, oldLogicalTop));
                        }
                    }

                    if (oldFloatingObject->originatingLine() && !selfNeedsLayout()) {
                        ASSERT(oldFloatingObject->originatingLine()->renderer() == this);
                        oldFloatingObject->originatingLine()->markDirty();
                    }

                    floatMap.remove(floatingObject->renderer());
                } else {
                    changeLogicalTop = 0;
                    changeLogicalBottom = std::max(changeLogicalBottom, logicalBottom);
                }
            }
        }

        RendererToFloatInfoMap::iterator end = floatMap.end();
        for (RendererToFloatInfoMap::iterator it = floatMap.begin(); it != end; ++it) {
            OwnPtr<FloatingObject>& floatingObject = it->value;
            if (!floatingObject->isDescendant()) {
                changeLogicalTop = 0;
                changeLogicalBottom = std::max(changeLogicalBottom, logicalBottomForFloat(floatingObject.get()));
            }
        }

        markLinesDirtyInBlockRange(changeLogicalTop, changeLogicalBottom);
    } else if (!oldIntrudingFloatSet.isEmpty()) {
        // If there are previously intruding floats that no longer intrude, then children with floats
        // should also get layout because they might need their floating object lists cleared.
        if (m_floatingObjects->set().size() < oldIntrudingFloatSet.size()) {
            markAllDescendantsWithFloatsForLayout();
        } else {
            const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
            FloatingObjectSetIterator end = floatingObjectSet.end();
            for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end && !oldIntrudingFloatSet.isEmpty(); ++it)
                oldIntrudingFloatSet.remove((*it)->renderer());
            if (!oldIntrudingFloatSet.isEmpty())
                markAllDescendantsWithFloatsForLayout();
        }
    }
}

void RenderBlockFlow::layoutBlockChildren(bool relayoutChildren, SubtreeLayoutScope& layoutScope, LayoutUnit beforeEdge, LayoutUnit afterEdge)
{
    dirtyForLayoutFromPercentageHeightDescendants(layoutScope);

    // The margin struct caches all our current margin collapsing state. The compact struct caches state when we encounter compacts,
    MarginInfo marginInfo(this, beforeEdge, afterEdge);

    // Fieldsets need to find their legend and position it inside the border of the object.
    // The legend then gets skipped during normal layout. The same is true for ruby text.
    // It doesn't get included in the normal layout process but is instead skipped.
    RenderObject* childToExclude = layoutSpecialExcludedChild(relayoutChildren, layoutScope);

    LayoutUnit previousFloatLogicalBottom = 0;

    RenderBox* next = firstChildBox();
    RenderBox* lastNormalFlowChild = 0;

    while (next) {
        RenderBox* child = next;
        next = child->nextSiblingBox();

        // FIXME: this should only be set from clearNeedsLayout crbug.com/361250
        child->setLayoutDidGetCalled(true);

        if (childToExclude == child)
            continue; // Skip this child, since it will be positioned by the specialized subclass (fieldsets and ruby runs).

        updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, child);

        if (child->isOutOfFlowPositioned()) {
            child->containingBlock()->insertPositionedObject(child);
            adjustPositionedBlock(child, marginInfo);
            continue;
        }
        if (child->isFloating()) {
            insertFloatingObject(child);
            adjustFloatingBlock(marginInfo);
            continue;
        }

        // Lay out the child.
        layoutBlockChild(child, marginInfo, previousFloatLogicalBottom);
        lastNormalFlowChild = child;
    }

    // Now do the handling of the bottom of the block, adding in our bottom border/padding and
    // determining the correct collapsed bottom margin information.
    handleAfterSideOfBlock(lastNormalFlowChild, beforeEdge, afterEdge, marginInfo);
}

// Our MarginInfo state used when laying out block children.
MarginInfo::MarginInfo(RenderBlockFlow* blockFlow, LayoutUnit beforeBorderPadding, LayoutUnit afterBorderPadding)
    : m_canCollapseMarginAfterWithLastChild(true)
    , m_atBeforeSideOfBlock(true)
    , m_atAfterSideOfBlock(false)
    , m_hasMarginBeforeQuirk(false)
    , m_hasMarginAfterQuirk(false)
    , m_determinedMarginBeforeQuirk(false)
    , m_discardMargin(false)
{
    RenderStyle* blockStyle = blockFlow->style();
    ASSERT(blockFlow->isRenderView() || blockFlow->parent());
    m_canCollapseWithChildren = !blockFlow->createsBlockFormattingContext() && !blockFlow->isRenderFlowThread() && !blockFlow->isRenderView();

    m_canCollapseMarginBeforeWithChildren = m_canCollapseWithChildren && !beforeBorderPadding && blockStyle->marginBeforeCollapse() != MSEPARATE;

    // If any height other than auto is specified in CSS, then we don't collapse our bottom
    // margins with our children's margins. To do otherwise would be to risk odd visual
    // effects when the children overflow out of the parent block and yet still collapse
    // with it. We also don't collapse if we have any bottom border/padding.
    m_canCollapseMarginAfterWithChildren = m_canCollapseWithChildren && !afterBorderPadding
        && (blockStyle->logicalHeight().isAuto() && !blockStyle->logicalHeight().value()) && blockStyle->marginAfterCollapse() != MSEPARATE;

    m_quirkContainer = blockFlow->isTableCell() || blockFlow->isBody();

    m_discardMargin = m_canCollapseMarginBeforeWithChildren && blockFlow->mustDiscardMarginBefore();

    m_positiveMargin = (m_canCollapseMarginBeforeWithChildren && !blockFlow->mustDiscardMarginBefore()) ? blockFlow->maxPositiveMarginBefore() : LayoutUnit();
    m_negativeMargin = (m_canCollapseMarginBeforeWithChildren && !blockFlow->mustDiscardMarginBefore()) ? blockFlow->maxNegativeMarginBefore() : LayoutUnit();
}

RenderBlockFlow::MarginValues RenderBlockFlow::marginValuesForChild(RenderBox* child) const
{
    LayoutUnit childBeforePositive = 0;
    LayoutUnit childBeforeNegative = 0;
    LayoutUnit childAfterPositive = 0;
    LayoutUnit childAfterNegative = 0;

    LayoutUnit beforeMargin = 0;
    LayoutUnit afterMargin = 0;

    RenderBlockFlow* childRenderBlockFlow = child->isRenderBlockFlow() ? toRenderBlockFlow(child) : 0;

    // If the child has the same directionality as we do, then we can just return its
    // margins in the same direction.
    if (!child->isWritingModeRoot()) {
        if (childRenderBlockFlow) {
            childBeforePositive = childRenderBlockFlow->maxPositiveMarginBefore();
            childBeforeNegative = childRenderBlockFlow->maxNegativeMarginBefore();
            childAfterPositive = childRenderBlockFlow->maxPositiveMarginAfter();
            childAfterNegative = childRenderBlockFlow->maxNegativeMarginAfter();
        } else {
            beforeMargin = child->marginBefore();
            afterMargin = child->marginAfter();
        }
    } else if (child->isHorizontalWritingMode() == isHorizontalWritingMode()) {
        // The child has a different directionality. If the child is parallel, then it's just
        // flipped relative to us. We can use the margins for the opposite edges.
        if (childRenderBlockFlow) {
            childBeforePositive = childRenderBlockFlow->maxPositiveMarginAfter();
            childBeforeNegative = childRenderBlockFlow->maxNegativeMarginAfter();
            childAfterPositive = childRenderBlockFlow->maxPositiveMarginBefore();
            childAfterNegative = childRenderBlockFlow->maxNegativeMarginBefore();
        } else {
            beforeMargin = child->marginAfter();
            afterMargin = child->marginBefore();
        }
    } else {
        // The child is perpendicular to us, which means its margins don't collapse but are on the
        // "logical left/right" sides of the child box. We can just return the raw margin in this case.
        beforeMargin = marginBeforeForChild(child);
        afterMargin = marginAfterForChild(child);
    }

    // Resolve uncollapsing margins into their positive/negative buckets.
    if (beforeMargin) {
        if (beforeMargin > 0)
            childBeforePositive = beforeMargin;
        else
            childBeforeNegative = -beforeMargin;
    }
    if (afterMargin) {
        if (afterMargin > 0)
            childAfterPositive = afterMargin;
        else
            childAfterNegative = -afterMargin;
    }

    return RenderBlockFlow::MarginValues(childBeforePositive, childBeforeNegative, childAfterPositive, childAfterNegative);
}

LayoutUnit RenderBlockFlow::collapseMargins(RenderBox* child, MarginInfo& marginInfo, bool childIsSelfCollapsing)
{
    bool childDiscardMarginBefore = mustDiscardMarginBeforeForChild(child);
    bool childDiscardMarginAfter = mustDiscardMarginAfterForChild(child);

    // The child discards the before margin when the the after margin has discard in the case of a self collapsing block.
    childDiscardMarginBefore = childDiscardMarginBefore || (childDiscardMarginAfter && childIsSelfCollapsing);

    // Get the four margin values for the child and cache them.
    const RenderBlockFlow::MarginValues childMargins = marginValuesForChild(child);

    // Get our max pos and neg top margins.
    LayoutUnit posTop = childMargins.positiveMarginBefore();
    LayoutUnit negTop = childMargins.negativeMarginBefore();

    // For self-collapsing blocks, collapse our bottom margins into our
    // top to get new posTop and negTop values.
    if (childIsSelfCollapsing) {
        posTop = std::max(posTop, childMargins.positiveMarginAfter());
        negTop = std::max(negTop, childMargins.negativeMarginAfter());
    }

    // See if the top margin is quirky. We only care if this child has
    // margins that will collapse with us.
    bool topQuirk = hasMarginBeforeQuirk(child);

    if (marginInfo.canCollapseWithMarginBefore()) {
        if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
            // This child is collapsing with the top of the
            // block. If it has larger margin values, then we need to update
            // our own maximal values.
            if (!document().inQuirksMode() || !marginInfo.quirkContainer() || !topQuirk)
                setMaxMarginBeforeValues(std::max(posTop, maxPositiveMarginBefore()), std::max(negTop, maxNegativeMarginBefore()));

            // The minute any of the margins involved isn't a quirk, don't
            // collapse it away, even if the margin is smaller (www.webreference.com
            // has an example of this, a <dt> with 0.8em author-specified inside
            // a <dl> inside a <td>.
            if (!marginInfo.determinedMarginBeforeQuirk() && !topQuirk && (posTop - negTop)) {
                setHasMarginBeforeQuirk(false);
                marginInfo.setDeterminedMarginBeforeQuirk(true);
            }

            if (!marginInfo.determinedMarginBeforeQuirk() && topQuirk && !marginBefore()) {
                // We have no top margin and our top child has a quirky margin.
                // We will pick up this quirky margin and pass it through.
                // This deals with the <td><div><p> case.
                // Don't do this for a block that split two inlines though. You do
                // still apply margins in this case.
                setHasMarginBeforeQuirk(true);
            }
        } else {
            // The before margin of the container will also discard all the margins it is collapsing with.
            setMustDiscardMarginBefore();
        }
    }

    // Once we find a child with discardMarginBefore all the margins collapsing with us must also discard.
    if (childDiscardMarginBefore) {
        marginInfo.setDiscardMargin(true);
        marginInfo.clearMargin();
    }

    if (marginInfo.quirkContainer() && marginInfo.atBeforeSideOfBlock() && (posTop - negTop))
        marginInfo.setHasMarginBeforeQuirk(topQuirk);

    LayoutUnit beforeCollapseLogicalTop = logicalHeight();
    LayoutUnit logicalTop = beforeCollapseLogicalTop;

    LayoutUnit clearanceForSelfCollapsingBlock;
    RenderObject* prev = child->previousSibling();
    RenderBlockFlow* previousBlockFlow =  prev && prev->isRenderBlockFlow() && !prev->isFloatingOrOutOfFlowPositioned() ? toRenderBlockFlow(prev) : 0;
    // If the child's previous sibling is a self-collapsing block that cleared a float then its top border edge has been set at the bottom border edge
    // of the float. Since we want to collapse the child's top margin with the self-collapsing block's top and bottom margins we need to adjust our parent's height to match the
    // margin top of the self-collapsing block. If the resulting collapsed margin leaves the child still intruding into the float then we will want to clear it.
    if (!marginInfo.canCollapseWithMarginBefore() && previousBlockFlow && previousBlockFlow->isSelfCollapsingBlock()) {
        clearanceForSelfCollapsingBlock = previousBlockFlow->marginOffsetForSelfCollapsingBlock();
        setLogicalHeight(logicalHeight() - clearanceForSelfCollapsingBlock);
    }

    if (childIsSelfCollapsing) {
        // For a self collapsing block both the before and after margins get discarded. The block doesn't contribute anything to the height of the block.
        // Also, the child's top position equals the logical height of the container.
        if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
            // This child has no height. We need to compute our
            // position before we collapse the child's margins together,
            // so that we can get an accurate position for the zero-height block.
            LayoutUnit collapsedBeforePos = std::max(marginInfo.positiveMargin(), childMargins.positiveMarginBefore());
            LayoutUnit collapsedBeforeNeg = std::max(marginInfo.negativeMargin(), childMargins.negativeMarginBefore());
            marginInfo.setMargin(collapsedBeforePos, collapsedBeforeNeg);

            // Now collapse the child's margins together, which means examining our
            // bottom margin values as well.
            marginInfo.setPositiveMarginIfLarger(childMargins.positiveMarginAfter());
            marginInfo.setNegativeMarginIfLarger(childMargins.negativeMarginAfter());

            if (!marginInfo.canCollapseWithMarginBefore()) {
                // We need to make sure that the position of the self-collapsing block
                // is correct, since it could have overflowing content
                // that needs to be positioned correctly (e.g., a block that
                // had a specified height of 0 but that actually had subcontent).
                logicalTop = logicalHeight() + collapsedBeforePos - collapsedBeforeNeg;
            }
        }
    } else {
        if (mustSeparateMarginBeforeForChild(child)) {
            ASSERT(!marginInfo.discardMargin() || (marginInfo.discardMargin() && !marginInfo.margin()));
            // If we are at the before side of the block and we collapse, ignore the computed margin
            // and just add the child margin to the container height. This will correctly position
            // the child inside the container.
            LayoutUnit separateMargin = !marginInfo.canCollapseWithMarginBefore() ? marginInfo.margin() : LayoutUnit(0);
            setLogicalHeight(logicalHeight() + separateMargin + marginBeforeForChild(child));
            logicalTop = logicalHeight();
        } else if (!marginInfo.discardMargin() && (!marginInfo.atBeforeSideOfBlock()
            || (!marginInfo.canCollapseMarginBeforeWithChildren()
            && (!document().inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.hasMarginBeforeQuirk())))) {
            // We're collapsing with a previous sibling's margins and not
            // with the top of the block.
            setLogicalHeight(logicalHeight() + std::max(marginInfo.positiveMargin(), posTop) - std::max(marginInfo.negativeMargin(), negTop));
            logicalTop = logicalHeight();
        }

        marginInfo.setDiscardMargin(childDiscardMarginAfter);

        if (!marginInfo.discardMargin()) {
            marginInfo.setPositiveMargin(childMargins.positiveMarginAfter());
            marginInfo.setNegativeMargin(childMargins.negativeMarginAfter());
        } else {
            marginInfo.clearMargin();
        }

        if (marginInfo.margin())
            marginInfo.setHasMarginAfterQuirk(hasMarginAfterQuirk(child));
    }

    // If margins would pull us past the top of the next page, then we need to pull back and pretend like the margins
    // collapsed into the page edge.
    LayoutState* layoutState = view()->layoutState();
    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop) {
        LayoutUnit oldLogicalTop = logicalTop;
        logicalTop = std::min(logicalTop, nextPageLogicalTop(beforeCollapseLogicalTop));
        setLogicalHeight(logicalHeight() + (logicalTop - oldLogicalTop));
    }

    if (previousBlockFlow) {
        // If |child| is a self-collapsing block it may have collapsed into a previous sibling and although it hasn't reduced the height of the parent yet
        // any floats from the parent will now overhang.
        LayoutUnit oldLogicalHeight = logicalHeight();
        setLogicalHeight(logicalTop);
        if (!previousBlockFlow->avoidsFloats() && (previousBlockFlow->logicalTop() + previousBlockFlow->lowestFloatLogicalBottom()) > logicalTop)
            addOverhangingFloats(previousBlockFlow, false);
        setLogicalHeight(oldLogicalHeight);

        // If |child|'s previous sibling is a self-collapsing block that cleared a float and margin collapsing resulted in |child| moving up
        // into the margin area of the self-collapsing block then the float it clears is now intruding into |child|. Layout again so that we can look for
        // floats in the parent that overhang |child|'s new logical top.
        bool logicalTopIntrudesIntoFloat = clearanceForSelfCollapsingBlock > 0 && logicalTop < beforeCollapseLogicalTop;
        if (logicalTopIntrudesIntoFloat && containsFloats() && !child->avoidsFloats() && lowestFloatLogicalBottom() > logicalTop)
            child->setNeedsLayoutAndFullPaintInvalidation();
    }

    return logicalTop;
}

void RenderBlockFlow::adjustPositionedBlock(RenderBox* child, const MarginInfo& marginInfo)
{
    bool isHorizontal = isHorizontalWritingMode();
    bool hasStaticBlockPosition = child->style()->hasStaticBlockPosition(isHorizontal);

    LayoutUnit logicalTop = logicalHeight();
    updateStaticInlinePositionForChild(child, logicalTop);

    if (!marginInfo.canCollapseWithMarginBefore()) {
        // Positioned blocks don't collapse margins, so add the margin provided by
        // the container now. The child's own margin is added later when calculating its logical top.
        LayoutUnit collapsedBeforePos = marginInfo.positiveMargin();
        LayoutUnit collapsedBeforeNeg = marginInfo.negativeMargin();
        logicalTop += collapsedBeforePos - collapsedBeforeNeg;
    }

    RenderLayer* childLayer = child->layer();
    if (childLayer->staticBlockPosition() != logicalTop) {
        childLayer->setStaticBlockPosition(logicalTop);
        if (hasStaticBlockPosition)
            child->setChildNeedsLayout(MarkOnlyThis);
    }
}

LayoutUnit RenderBlockFlow::clearFloatsIfNeeded(RenderBox* child, MarginInfo& marginInfo, LayoutUnit oldTopPosMargin, LayoutUnit oldTopNegMargin, LayoutUnit yPos, bool childIsSelfCollapsing)
{
    LayoutUnit heightIncrease = getClearDelta(child, yPos);
    if (!heightIncrease)
        return yPos;

    if (childIsSelfCollapsing) {
        bool childDiscardMargin = mustDiscardMarginBeforeForChild(child) || mustDiscardMarginAfterForChild(child);

        // For self-collapsing blocks that clear, they can still collapse their
        // margins with following siblings. Reset the current margins to represent
        // the self-collapsing block's margins only.
        // If DISCARD is specified for -webkit-margin-collapse, reset the margin values.
        RenderBlockFlow::MarginValues childMargins = marginValuesForChild(child);
        if (!childDiscardMargin) {
            marginInfo.setPositiveMargin(std::max(childMargins.positiveMarginBefore(), childMargins.positiveMarginAfter()));
            marginInfo.setNegativeMargin(std::max(childMargins.negativeMarginBefore(), childMargins.negativeMarginAfter()));
        } else {
            marginInfo.clearMargin();
        }
        marginInfo.setDiscardMargin(childDiscardMargin);

        // CSS2.1 states:
        // "If the top and bottom margins of an element with clearance are adjoining, its margins collapse with
        // the adjoining margins of following siblings but that resulting margin does not collapse with the bottom margin of the parent block."
        // So the parent's bottom margin cannot collapse through this block or any subsequent self-collapsing blocks. Set a bit to ensure
        // this happens; it will get reset if we encounter an in-flow sibling that is not self-collapsing.
        marginInfo.setCanCollapseMarginAfterWithLastChild(false);

        // For now set the border-top of |child| flush with the bottom border-edge of the float so it can layout any floating or positioned children of
        // its own at the correct vertical position. If subsequent siblings attempt to collapse with |child|'s margins in |collapseMargins| we will
        // adjust the height of the parent to |child|'s margin top (which if it is positive sits up 'inside' the float it's clearing) so that all three
        // margins can collapse at the correct vertical position.
        // Per CSS2.1 we need to ensure that any negative margin-top clears |child| beyond the bottom border-edge of the float so that the top border edge of the child
        // (i.e. its clearance)  is at a position that satisfies the equation: "the amount of clearance is set so that clearance + margin-top = [height of float],
        // i.e., clearance = [height of float] - margin-top".
        setLogicalHeight(child->logicalTop() + childMargins.negativeMarginBefore());
    } else {
        // Increase our height by the amount we had to clear.
        setLogicalHeight(logicalHeight() + heightIncrease);
    }

    if (marginInfo.canCollapseWithMarginBefore()) {
        // We can no longer collapse with the top of the block since a clear
        // occurred. The empty blocks collapse into the cleared block.
        setMaxMarginBeforeValues(oldTopPosMargin, oldTopNegMargin);
        marginInfo.setAtBeforeSideOfBlock(false);

        // In case the child discarded the before margin of the block we need to reset the mustDiscardMarginBefore flag to the initial value.
        setMustDiscardMarginBefore(style()->marginBeforeCollapse() == MDISCARD);
    }

    return yPos + heightIncrease;
}

void RenderBlockFlow::setCollapsedBottomMargin(const MarginInfo& marginInfo)
{
    if (marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()) {
        // Update the after side margin of the container to discard if the after margin of the last child also discards and we collapse with it.
        // Don't update the max margin values because we won't need them anyway.
        if (marginInfo.discardMargin()) {
            setMustDiscardMarginAfter();
            return;
        }

        // Update our max pos/neg bottom margins, since we collapsed our bottom margins
        // with our children.
        setMaxMarginAfterValues(std::max(maxPositiveMarginAfter(), marginInfo.positiveMargin()), std::max(maxNegativeMarginAfter(), marginInfo.negativeMargin()));

        if (!marginInfo.hasMarginAfterQuirk())
            setHasMarginAfterQuirk(false);

        if (marginInfo.hasMarginAfterQuirk() && !marginAfter()) {
            // We have no bottom margin and our last child has a quirky margin.
            // We will pick up this quirky margin and pass it through.
            // This deals with the <td><div><p> case.
            setHasMarginAfterQuirk(true);
        }
    }
}

void RenderBlockFlow::marginBeforeEstimateForChild(RenderBox* child, LayoutUnit& positiveMarginBefore, LayoutUnit& negativeMarginBefore, bool& discardMarginBefore) const
{
    // Give up if in quirks mode and we're a body/table cell and the top margin of the child box is quirky.
    // Give up if the child specified -webkit-margin-collapse: separate that prevents collapsing.
    // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
    if ((document().inQuirksMode() && hasMarginBeforeQuirk(child) && (isTableCell() || isBody())) || child->style()->marginBeforeCollapse() == MSEPARATE)
        return;

    // The margins are discarded by a child that specified -webkit-margin-collapse: discard.
    // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
    if (child->style()->marginBeforeCollapse() == MDISCARD) {
        positiveMarginBefore = 0;
        negativeMarginBefore = 0;
        discardMarginBefore = true;
        return;
    }

    LayoutUnit beforeChildMargin = marginBeforeForChild(child);
    positiveMarginBefore = std::max(positiveMarginBefore, beforeChildMargin);
    negativeMarginBefore = std::max(negativeMarginBefore, -beforeChildMargin);

    if (!child->isRenderBlockFlow())
        return;

    RenderBlockFlow* childBlockFlow = toRenderBlockFlow(child);
    if (childBlockFlow->childrenInline() || childBlockFlow->isWritingModeRoot())
        return;

    MarginInfo childMarginInfo(childBlockFlow, childBlockFlow->borderBefore() + childBlockFlow->paddingBefore(), childBlockFlow->borderAfter() + childBlockFlow->paddingAfter());
    if (!childMarginInfo.canCollapseMarginBeforeWithChildren())
        return;

    RenderBox* grandchildBox = childBlockFlow->firstChildBox();
    for ( ; grandchildBox; grandchildBox = grandchildBox->nextSiblingBox()) {
        if (!grandchildBox->isFloatingOrOutOfFlowPositioned())
            break;
    }

    // Give up if there is clearance on the box, since it probably won't collapse into us.
    if (!grandchildBox || grandchildBox->style()->clear() != CNONE)
        return;

    // Make sure to update the block margins now for the grandchild box so that we're looking at current values.
    if (grandchildBox->needsLayout()) {
        grandchildBox->computeAndSetBlockDirectionMargins(this);
        if (grandchildBox->isRenderBlock()) {
            RenderBlock* grandchildBlock = toRenderBlock(grandchildBox);
            grandchildBlock->setHasMarginBeforeQuirk(grandchildBox->style()->hasMarginBeforeQuirk());
            grandchildBlock->setHasMarginAfterQuirk(grandchildBox->style()->hasMarginAfterQuirk());
        }
    }

    // Collapse the margin of the grandchild box with our own to produce an estimate.
    childBlockFlow->marginBeforeEstimateForChild(grandchildBox, positiveMarginBefore, negativeMarginBefore, discardMarginBefore);
}

LayoutUnit RenderBlockFlow::estimateLogicalTopPosition(RenderBox* child, const MarginInfo& marginInfo, LayoutUnit& estimateWithoutPagination)
{
    // FIXME: We need to eliminate the estimation of vertical position, because when it's wrong we sometimes trigger a pathological
    // relayout if there are intruding floats.
    LayoutUnit logicalTopEstimate = logicalHeight();
    if (!marginInfo.canCollapseWithMarginBefore()) {
        LayoutUnit positiveMarginBefore = 0;
        LayoutUnit negativeMarginBefore = 0;
        bool discardMarginBefore = false;
        if (child->selfNeedsLayout()) {
            // Try to do a basic estimation of how the collapse is going to go.
            marginBeforeEstimateForChild(child, positiveMarginBefore, negativeMarginBefore, discardMarginBefore);
        } else {
            // Use the cached collapsed margin values from a previous layout. Most of the time they
            // will be right.
            RenderBlockFlow::MarginValues marginValues = marginValuesForChild(child);
            positiveMarginBefore = std::max(positiveMarginBefore, marginValues.positiveMarginBefore());
            negativeMarginBefore = std::max(negativeMarginBefore, marginValues.negativeMarginBefore());
            discardMarginBefore = mustDiscardMarginBeforeForChild(child);
        }

        // Collapse the result with our current margins.
        if (!discardMarginBefore)
            logicalTopEstimate += std::max(marginInfo.positiveMargin(), positiveMarginBefore) - std::max(marginInfo.negativeMargin(), negativeMarginBefore);
    }

    // Adjust logicalTopEstimate down to the next page if the margins are so large that we don't fit on the current
    // page.
    LayoutState* layoutState = view()->layoutState();
    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight())
        logicalTopEstimate = std::min(logicalTopEstimate, nextPageLogicalTop(logicalHeight()));

    logicalTopEstimate += getClearDelta(child, logicalTopEstimate);

    estimateWithoutPagination = logicalTopEstimate;

    if (layoutState->isPaginated()) {
        // If the object has a page or column break value of "before", then we should shift to the top of the next page.
        logicalTopEstimate = applyBeforeBreak(child, logicalTopEstimate);

        // For replaced elements and scrolled elements, we want to shift them to the next page if they don't fit on the current one.
        logicalTopEstimate = adjustForUnsplittableChild(child, logicalTopEstimate);

        if (!child->selfNeedsLayout() && child->isRenderBlockFlow())
            logicalTopEstimate += toRenderBlockFlow(child)->paginationStrut();
    }

    return logicalTopEstimate;
}

LayoutUnit RenderBlockFlow::marginOffsetForSelfCollapsingBlock()
{
    ASSERT(isSelfCollapsingBlock());
    RenderBlockFlow* parentBlock = toRenderBlockFlow(parent());
    if (parentBlock && style()->clear() && parentBlock->getClearDelta(this, logicalHeight()))
        return marginValuesForChild(this).positiveMarginBefore();
    return LayoutUnit();
}

void RenderBlockFlow::adjustFloatingBlock(const MarginInfo& marginInfo)
{
    // The float should be positioned taking into account the bottom margin
    // of the previous flow. We add that margin into the height, get the
    // float positioned properly, and then subtract the margin out of the
    // height again. In the case of self-collapsing blocks, we always just
    // use the top margins, since the self-collapsing block collapsed its
    // own bottom margin into its top margin.
    //
    // Note also that the previous flow may collapse its margin into the top of
    // our block. If this is the case, then we do not add the margin in to our
    // height when computing the position of the float. This condition can be tested
    // for by simply calling canCollapseWithMarginBefore. See
    // http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/046.html for
    // an example of this scenario.
    LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? LayoutUnit() : marginInfo.margin();
    setLogicalHeight(logicalHeight() + marginOffset);
    positionNewFloats();
    setLogicalHeight(logicalHeight() - marginOffset);
}

void RenderBlockFlow::handleAfterSideOfBlock(RenderBox* lastChild, LayoutUnit beforeSide, LayoutUnit afterSide, MarginInfo& marginInfo)
{
    marginInfo.setAtAfterSideOfBlock(true);

    // If our last child was a self-collapsing block with clearance then our logical height is flush with the
    // bottom edge of the float that the child clears. The correct vertical position for the margin-collapsing we want
    // to perform now is at the child's margin-top - so adjust our height to that position.
    if (lastChild && lastChild->isRenderBlockFlow() && lastChild->isSelfCollapsingBlock())
        setLogicalHeight(logicalHeight() - toRenderBlockFlow(lastChild)->marginOffsetForSelfCollapsingBlock());

    if (marginInfo.canCollapseMarginAfterWithChildren() && !marginInfo.canCollapseMarginAfterWithLastChild())
        marginInfo.setCanCollapseMarginAfterWithChildren(false);

    // If we can't collapse with children then go ahead and add in the bottom margin.
    if (!marginInfo.discardMargin() && (!marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()
        && (!document().inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.hasMarginAfterQuirk())))
        setLogicalHeight(logicalHeight() + marginInfo.margin());

    // Now add in our bottom border/padding.
    setLogicalHeight(logicalHeight() + afterSide);

    // Negative margins can cause our height to shrink below our minimal height (border/padding).
    // If this happens, ensure that the computed height is increased to the minimal height.
    setLogicalHeight(std::max(logicalHeight(), beforeSide + afterSide));

    // Update our bottom collapsed margin info.
    setCollapsedBottomMargin(marginInfo);
}

void RenderBlockFlow::setMustDiscardMarginBefore(bool value)
{
    if (style()->marginBeforeCollapse() == MDISCARD) {
        ASSERT(value);
        return;
    }

    if (!m_rareData && !value)
        return;

    if (!m_rareData)
        m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));

    m_rareData->m_discardMarginBefore = value;
}

void RenderBlockFlow::setMustDiscardMarginAfter(bool value)
{
    if (style()->marginAfterCollapse() == MDISCARD) {
        ASSERT(value);
        return;
    }

    if (!m_rareData && !value)
        return;

    if (!m_rareData)
        m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));

    m_rareData->m_discardMarginAfter = value;
}

bool RenderBlockFlow::mustDiscardMarginBefore() const
{
    return style()->marginBeforeCollapse() == MDISCARD || (m_rareData && m_rareData->m_discardMarginBefore);
}

bool RenderBlockFlow::mustDiscardMarginAfter() const
{
    return style()->marginAfterCollapse() == MDISCARD || (m_rareData && m_rareData->m_discardMarginAfter);
}

bool RenderBlockFlow::mustDiscardMarginBeforeForChild(const RenderBox* child) const
{
    ASSERT(!child->selfNeedsLayout());
    if (!child->isWritingModeRoot())
        return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginBefore() : (child->style()->marginBeforeCollapse() == MDISCARD);
    if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
        return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginAfter() : (child->style()->marginAfterCollapse() == MDISCARD);

    // FIXME: We return false here because the implementation is not geometrically complete. We have values only for before/after, not start/end.
    // In case the boxes are perpendicular we assume the property is not specified.
    return false;
}

bool RenderBlockFlow::mustDiscardMarginAfterForChild(const RenderBox* child) const
{
    ASSERT(!child->selfNeedsLayout());
    if (!child->isWritingModeRoot())
        return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginAfter() : (child->style()->marginAfterCollapse() == MDISCARD);
    if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
        return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginBefore() : (child->style()->marginBeforeCollapse() == MDISCARD);

    // FIXME: See |mustDiscardMarginBeforeForChild| above.
    return false;
}

void RenderBlockFlow::setMaxMarginBeforeValues(LayoutUnit pos, LayoutUnit neg)
{
    if (!m_rareData) {
        if (pos == RenderBlockFlowRareData::positiveMarginBeforeDefault(this) && neg == RenderBlockFlowRareData::negativeMarginBeforeDefault(this))
            return;
        m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
    }
    m_rareData->m_margins.setPositiveMarginBefore(pos);
    m_rareData->m_margins.setNegativeMarginBefore(neg);
}

void RenderBlockFlow::setMaxMarginAfterValues(LayoutUnit pos, LayoutUnit neg)
{
    if (!m_rareData) {
        if (pos == RenderBlockFlowRareData::positiveMarginAfterDefault(this) && neg == RenderBlockFlowRareData::negativeMarginAfterDefault(this))
            return;
        m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
    }
    m_rareData->m_margins.setPositiveMarginAfter(pos);
    m_rareData->m_margins.setNegativeMarginAfter(neg);
}

bool RenderBlockFlow::mustSeparateMarginBeforeForChild(const RenderBox* child) const
{
    ASSERT(!child->selfNeedsLayout());
    const RenderStyle* childStyle = child->style();
    if (!child->isWritingModeRoot())
        return childStyle->marginBeforeCollapse() == MSEPARATE;
    if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
        return childStyle->marginAfterCollapse() == MSEPARATE;

    // FIXME: See |mustDiscardMarginBeforeForChild| above.
    return false;
}

bool RenderBlockFlow::mustSeparateMarginAfterForChild(const RenderBox* child) const
{
    ASSERT(!child->selfNeedsLayout());
    const RenderStyle* childStyle = child->style();
    if (!child->isWritingModeRoot())
        return childStyle->marginAfterCollapse() == MSEPARATE;
    if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
        return childStyle->marginBeforeCollapse() == MSEPARATE;

    // FIXME: See |mustDiscardMarginBeforeForChild| above.
    return false;
}

LayoutUnit RenderBlockFlow::applyBeforeBreak(RenderBox* child, LayoutUnit logicalOffset)
{
    // FIXME: Add page break checking here when we support printing.
    RenderFlowThread* flowThread = flowThreadContainingBlock();
    bool isInsideMulticolFlowThread = flowThread;
    bool checkColumnBreaks = isInsideMulticolFlowThread || view()->layoutState()->isPaginatingColumns();
    bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight(); // FIXME: Once columns can print we have to check this.
    bool checkBeforeAlways = (checkColumnBreaks && child->style()->columnBreakBefore() == PBALWAYS)
        || (checkPageBreaks && child->style()->pageBreakBefore() == PBALWAYS);
    if (checkBeforeAlways && inNormalFlow(child)) {
        if (checkColumnBreaks) {
            if (isInsideMulticolFlowThread) {
                LayoutUnit offsetBreakAdjustment = 0;
                if (flowThread->addForcedRegionBreak(offsetFromLogicalTopOfFirstPage() + logicalOffset, child, true, &offsetBreakAdjustment))
                    return logicalOffset + offsetBreakAdjustment;
            } else {
                view()->layoutState()->addForcedColumnBreak(*child, logicalOffset);
            }
        }
        return nextPageLogicalTop(logicalOffset, IncludePageBoundary);
    }
    return logicalOffset;
}

LayoutUnit RenderBlockFlow::applyAfterBreak(RenderBox* child, LayoutUnit logicalOffset, MarginInfo& marginInfo)
{
    // FIXME: Add page break checking here when we support printing.
    RenderFlowThread* flowThread = flowThreadContainingBlock();
    bool isInsideMulticolFlowThread = flowThread;
    bool checkColumnBreaks = isInsideMulticolFlowThread || view()->layoutState()->isPaginatingColumns();
    bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight(); // FIXME: Once columns can print we have to check this.
    bool checkAfterAlways = (checkColumnBreaks && child->style()->columnBreakAfter() == PBALWAYS)
        || (checkPageBreaks && child->style()->pageBreakAfter() == PBALWAYS);
    if (checkAfterAlways && inNormalFlow(child)) {
        LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? LayoutUnit() : marginInfo.margin();

        // So our margin doesn't participate in the next collapsing steps.
        marginInfo.clearMargin();

        if (checkColumnBreaks) {
            if (isInsideMulticolFlowThread) {
                LayoutUnit offsetBreakAdjustment = 0;
                if (flowThread->addForcedRegionBreak(offsetFromLogicalTopOfFirstPage() + logicalOffset + marginOffset, child, false, &offsetBreakAdjustment))
                    return logicalOffset + marginOffset + offsetBreakAdjustment;
            } else {
                view()->layoutState()->addForcedColumnBreak(*child, logicalOffset);
            }
        }
        return nextPageLogicalTop(logicalOffset, IncludePageBoundary);
    }
    return logicalOffset;
}

void RenderBlockFlow::addOverflowFromFloats()
{
    if (!m_floatingObjects)
        return;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* floatingObject = it->get();
        if (floatingObject->isDescendant())
            addOverflowFromChild(floatingObject->renderer(), IntSize(xPositionForFloatIncludingMargin(floatingObject), yPositionForFloatIncludingMargin(floatingObject)));
    }
}

void RenderBlockFlow::computeOverflow(LayoutUnit oldClientAfterEdge, bool recomputeFloats)
{
    RenderBlock::computeOverflow(oldClientAfterEdge, recomputeFloats);
    if (!hasColumns() && (recomputeFloats || createsBlockFormattingContext() || hasSelfPaintingLayer()))
        addOverflowFromFloats();
}

RootInlineBox* RenderBlockFlow::createAndAppendRootInlineBox()
{
    RootInlineBox* rootBox = createRootInlineBox();
    m_lineBoxes.appendLineBox(rootBox);

    return rootBox;
}

void RenderBlockFlow::deleteLineBoxTree()
{
    if (containsFloats())
        m_floatingObjects->clearLineBoxTreePointers();

    m_lineBoxes.deleteLineBoxTree();
}

void RenderBlockFlow::markAllDescendantsWithFloatsForLayout(RenderBox* floatToRemove, bool inLayout)
{
    if (!everHadLayout() && !containsFloats())
        return;

    if (m_descendantsWithFloatsMarkedForLayout && !floatToRemove)
        return;
    m_descendantsWithFloatsMarkedForLayout |= !floatToRemove;

    MarkingBehavior markParents = inLayout ? MarkOnlyThis : MarkContainingBlockChain;
    setChildNeedsLayout(markParents);

    if (floatToRemove)
        removeFloatingObject(floatToRemove);

    // Iterate over our children and mark them as needed.
    if (!childrenInline()) {
        for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
            if ((!floatToRemove && child->isFloatingOrOutOfFlowPositioned()) || !child->isRenderBlock())
                continue;
            if (!child->isRenderBlockFlow()) {
                RenderBlock* childBlock = toRenderBlock(child);
                if (childBlock->shrinkToAvoidFloats() && childBlock->everHadLayout())
                    childBlock->setChildNeedsLayout(markParents);
                continue;
            }
            RenderBlockFlow* childBlockFlow = toRenderBlockFlow(child);
            if ((floatToRemove ? childBlockFlow->containsFloat(floatToRemove) : childBlockFlow->containsFloats()) || childBlockFlow->shrinkToAvoidFloats())
                childBlockFlow->markAllDescendantsWithFloatsForLayout(floatToRemove, inLayout);
        }
    }
}

void RenderBlockFlow::markSiblingsWithFloatsForLayout(RenderBox* floatToRemove)
{
    if (!m_floatingObjects)
        return;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();

    for (RenderObject* next = nextSibling(); next; next = next->nextSibling()) {
        if (!next->isRenderBlockFlow() || next->isFloatingOrOutOfFlowPositioned() || toRenderBlockFlow(next)->avoidsFloats())
            continue;

        RenderBlockFlow* nextBlock = toRenderBlockFlow(next);
        for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
            RenderBox* floatingBox = (*it)->renderer();
            if (floatToRemove && floatingBox != floatToRemove)
                continue;
            if (nextBlock->containsFloat(floatingBox))
                nextBlock->markAllDescendantsWithFloatsForLayout(floatingBox);
        }
    }
}

LayoutUnit RenderBlockFlow::getClearDelta(RenderBox* child, LayoutUnit logicalTop)
{
    // There is no need to compute clearance if we have no floats.
    if (!containsFloats())
        return 0;

    // At least one float is present. We need to perform the clearance computation.
    bool clearSet = child->style()->clear() != CNONE;
    LayoutUnit logicalBottom = 0;
    switch (child->style()->clear()) {
    case CNONE:
        break;
    case CLEFT:
        logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
        break;
    case CRIGHT:
        logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatRight);
        break;
    case CBOTH:
        logicalBottom = lowestFloatLogicalBottom();
        break;
    }

    // We also clear floats if we are too big to sit on the same line as a float (and wish to avoid floats by default).
    LayoutUnit result = clearSet ? std::max<LayoutUnit>(0, logicalBottom - logicalTop) : LayoutUnit();
    if (!result && child->avoidsFloats()) {
        LayoutUnit newLogicalTop = logicalTop;
        while (true) {
            LayoutUnit availableLogicalWidthAtNewLogicalTopOffset = availableLogicalWidthForLine(newLogicalTop, false, logicalHeightForChild(child));
            if (availableLogicalWidthAtNewLogicalTopOffset == availableLogicalWidthForContent())
                return newLogicalTop - logicalTop;

            LayoutRect borderBox = child->borderBoxRect();
            LayoutUnit childLogicalWidthAtOldLogicalTopOffset = isHorizontalWritingMode() ? borderBox.width() : borderBox.height();

            // FIXME: None of this is right for perpendicular writing-mode children.
            LayoutUnit childOldLogicalWidth = child->logicalWidth();
            LayoutUnit childOldMarginLeft = child->marginLeft();
            LayoutUnit childOldMarginRight = child->marginRight();
            LayoutUnit childOldLogicalTop = child->logicalTop();

            child->setLogicalTop(newLogicalTop);
            child->updateLogicalWidth();
            borderBox = child->borderBoxRect();
            LayoutUnit childLogicalWidthAtNewLogicalTopOffset = isHorizontalWritingMode() ? borderBox.width() : borderBox.height();

            child->setLogicalTop(childOldLogicalTop);
            child->setLogicalWidth(childOldLogicalWidth);
            child->setMarginLeft(childOldMarginLeft);
            child->setMarginRight(childOldMarginRight);

            if (childLogicalWidthAtNewLogicalTopOffset <= availableLogicalWidthAtNewLogicalTopOffset) {
                // Even though we may not be moving, if the logical width did shrink because of the presence of new floats, then
                // we need to force a relayout as though we shifted. This happens because of the dynamic addition of overhanging floats
                // from previous siblings when negative margins exist on a child (see the addOverhangingFloats call at the end of collapseMargins).
                if (childLogicalWidthAtOldLogicalTopOffset != childLogicalWidthAtNewLogicalTopOffset)
                    child->setChildNeedsLayout(MarkOnlyThis);
                return newLogicalTop - logicalTop;
            }

            newLogicalTop = nextFloatLogicalBottomBelow(newLogicalTop);
            ASSERT(newLogicalTop >= logicalTop);
            if (newLogicalTop < logicalTop)
                break;
        }
        ASSERT_NOT_REACHED();
    }
    return result;
}

void RenderBlockFlow::createFloatingObjects()
{
    m_floatingObjects = adoptPtr(new FloatingObjects(this, isHorizontalWritingMode()));
}

void RenderBlockFlow::styleWillChange(StyleDifference diff, const RenderStyle& newStyle)
{
    RenderStyle* oldStyle = style();
    s_canPropagateFloatIntoSibling = oldStyle ? !isFloatingOrOutOfFlowPositioned() && !avoidsFloats() : false;
    if (oldStyle && parent() && diff.needsFullLayout() && oldStyle->position() != newStyle.position()
        && containsFloats() && !isFloating() && !isOutOfFlowPositioned() && newStyle.hasOutOfFlowPosition())
            markAllDescendantsWithFloatsForLayout();

    RenderBlock::styleWillChange(diff, newStyle);
}

void RenderBlockFlow::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
{
    RenderBlock::styleDidChange(diff, oldStyle);

    // After our style changed, if we lose our ability to propagate floats into next sibling
    // blocks, then we need to find the top most parent containing that overhanging float and
    // then mark its descendants with floats for layout and clear all floats from its next
    // sibling blocks that exist in our floating objects list. See bug 56299 and 62875.
    bool canPropagateFloatIntoSibling = !isFloatingOrOutOfFlowPositioned() && !avoidsFloats();
    if (diff.needsFullLayout() && s_canPropagateFloatIntoSibling && !canPropagateFloatIntoSibling && hasOverhangingFloats()) {
        RenderBlockFlow* parentBlockFlow = this;
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator end = floatingObjectSet.end();

        for (RenderObject* curr = parent(); curr && !curr->isRenderView(); curr = curr->parent()) {
            if (curr->isRenderBlockFlow()) {
                RenderBlockFlow* currBlock = toRenderBlockFlow(curr);

                if (currBlock->hasOverhangingFloats()) {
                    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
                        RenderBox* renderer = (*it)->renderer();
                        if (currBlock->hasOverhangingFloat(renderer)) {
                            parentBlockFlow = currBlock;
                            break;
                        }
                    }
                }
            }
        }

        parentBlockFlow->markAllDescendantsWithFloatsForLayout();
        parentBlockFlow->markSiblingsWithFloatsForLayout();
    }

    if (diff.needsFullLayout() || !oldStyle)
        createOrDestroyMultiColumnFlowThreadIfNeeded(oldStyle);
}

void RenderBlockFlow::updateStaticInlinePositionForChild(RenderBox* child, LayoutUnit logicalTop)
{
    if (child->style()->isOriginalDisplayInlineType())
        setStaticInlinePositionForChild(child, startAlignedOffsetForLine(logicalTop, false));
    else
        setStaticInlinePositionForChild(child, startOffsetForContent());
}

void RenderBlockFlow::setStaticInlinePositionForChild(RenderBox* child, LayoutUnit inlinePosition)
{
    child->layer()->setStaticInlinePosition(inlinePosition);
}

void RenderBlockFlow::addChild(RenderObject* newChild, RenderObject* beforeChild)
{
    if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
        flowThread->addChild(newChild, beforeChild);
        return;
    }
    RenderBlock::addChild(newChild, beforeChild);
}

void RenderBlockFlow::moveAllChildrenIncludingFloatsTo(RenderBlock* toBlock, bool fullRemoveInsert)
{
    RenderBlockFlow* toBlockFlow = toRenderBlockFlow(toBlock);
    moveAllChildrenTo(toBlockFlow, fullRemoveInsert);

    // When a portion of the render tree is being detached, anonymous blocks
    // will be combined as their children are deleted. In this process, the
    // anonymous block later in the tree is merged into the one preceeding it.
    // It can happen that the later block (this) contains floats that the
    // previous block (toBlockFlow) did not contain, and thus are not in the
    // floating objects list for toBlockFlow. This can result in toBlockFlow containing
    // floats that are not in it's floating objects list, but are in the
    // floating objects lists of siblings and parents. This can cause problems
    // when the float itself is deleted, since the deletion code assumes that
    // if a float is not in it's containing block's floating objects list, it
    // isn't in any floating objects list. In order to preserve this condition
    // (removing it has serious performance implications), we need to copy the
    // floating objects from the old block (this) to the new block (toBlockFlow).
    // The float's metrics will likely all be wrong, but since toBlockFlow is
    // already marked for layout, this will get fixed before anything gets
    // displayed.
    // See bug https://code.google.com/p/chromium/issues/detail?id=230907
    if (m_floatingObjects) {
        if (!toBlockFlow->m_floatingObjects)
            toBlockFlow->createFloatingObjects();

        const FloatingObjectSet& fromFloatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator end = fromFloatingObjectSet.end();

        for (FloatingObjectSetIterator it = fromFloatingObjectSet.begin(); it != end; ++it) {
            FloatingObject* floatingObject = it->get();

            // Don't insert the object again if it's already in the list
            if (toBlockFlow->containsFloat(floatingObject->renderer()))
                continue;

            toBlockFlow->m_floatingObjects->add(floatingObject->unsafeClone());
        }
    }

}

void RenderBlockFlow::invalidatePaintForOverhangingFloats(bool paintAllDescendants)
{
    // Invalidate paint of any overhanging floats (if we know we're the one to paint them).
    // Otherwise, bail out.
    if (!hasOverhangingFloats())
        return;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* floatingObject = it->get();
        // Only issue paint invaldiations for the object if it is overhanging, is not in its own layer, and
        // is our responsibility to paint (m_shouldPaint is set). When paintAllDescendants is true, the latter
        // condition is replaced with being a descendant of us.
        if (logicalBottomForFloat(floatingObject) > logicalHeight()
            && !floatingObject->renderer()->hasSelfPaintingLayer()
            && (floatingObject->shouldPaint() || (paintAllDescendants && floatingObject->renderer()->isDescendantOf(this)))) {

            RenderBox* floatingRenderer = floatingObject->renderer();
            floatingRenderer->setShouldDoFullPaintInvalidation(true);
            floatingRenderer->invalidatePaintForOverhangingFloats(false);
        }
    }
}

void RenderBlockFlow::invalidatePaintForOverflow()
{
    // FIXME: We could tighten up the left and right invalidation points if we let layoutInlineChildren fill them in based off the particular lines
    // it had to lay out. We wouldn't need the hasOverflowClip() hack in that case either.
    LayoutUnit paintInvalidationLogicalLeft = logicalLeftVisualOverflow();
    LayoutUnit paintInvalidationLogicalRight = logicalRightVisualOverflow();
    if (hasOverflowClip()) {
        // If we have clipped overflow, we should use layout overflow as well, since visual overflow from lines didn't propagate to our block's overflow.
        // Note the old code did this as well but even for overflow:visible. The addition of hasOverflowClip() at least tightens up the hack a bit.
        // layoutInlineChildren should be patched to compute the entire paint invalidation rect.
        paintInvalidationLogicalLeft = std::min(paintInvalidationLogicalLeft, logicalLeftLayoutOverflow());
        paintInvalidationLogicalRight = std::max(paintInvalidationLogicalRight, logicalRightLayoutOverflow());
    }

    LayoutRect paintInvalidationRect;
    if (isHorizontalWritingMode())
        paintInvalidationRect = LayoutRect(paintInvalidationLogicalLeft, m_paintInvalidationLogicalTop, paintInvalidationLogicalRight - paintInvalidationLogicalLeft, m_paintInvalidationLogicalBottom - m_paintInvalidationLogicalTop);
    else
        paintInvalidationRect = LayoutRect(m_paintInvalidationLogicalTop, paintInvalidationLogicalLeft, m_paintInvalidationLogicalBottom - m_paintInvalidationLogicalTop, paintInvalidationLogicalRight - paintInvalidationLogicalLeft);

    // The paint invalidation rect may be split across columns, in which case adjustRectForColumns() will return the union.
    adjustRectForColumns(paintInvalidationRect);

    if (hasOverflowClip()) {
        // Adjust the paint invalidation rect for scroll offset
        paintInvalidationRect.move(-scrolledContentOffset());

        // Don't allow this rect to spill out of our overflow box.
        paintInvalidationRect.intersect(LayoutRect(LayoutPoint(), size()));
    }

    // Make sure the rect is still non-empty after intersecting for overflow above
    if (!paintInvalidationRect.isEmpty()) {
        // Hits in media/event-attributes.html
        DisableCompositingQueryAsserts disabler;

        invalidatePaintRectangle(paintInvalidationRect); // We need to do a partial paint invalidation of our content.
        if (hasReflection())
            invalidatePaintRectangle(reflectedRect(paintInvalidationRect));
    }

    m_paintInvalidationLogicalTop = 0;
    m_paintInvalidationLogicalBottom = 0;
}

void RenderBlockFlow::paintFloats(PaintInfo& paintInfo, const LayoutPoint& paintOffset, bool preservePhase)
{
    BlockFlowPainter(*this).paintFloats(paintInfo, paintOffset, preservePhase);
}

void RenderBlockFlow::clipOutFloatingObjects(const RenderBlock* rootBlock, const PaintInfo* paintInfo, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock) const
{
    if (m_floatingObjects) {
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator end = floatingObjectSet.end();
        for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
            FloatingObject* floatingObject = it->get();
            LayoutRect floatBox(offsetFromRootBlock.width() + xPositionForFloatIncludingMargin(floatingObject),
                offsetFromRootBlock.height() + yPositionForFloatIncludingMargin(floatingObject),
                floatingObject->renderer()->width(), floatingObject->renderer()->height());
            rootBlock->flipForWritingMode(floatBox);
            floatBox.move(rootBlockPhysicalPosition.x(), rootBlockPhysicalPosition.y());
            paintInfo->context->clipOut(pixelSnappedIntRect(floatBox));
        }
    }
}

void RenderBlockFlow::clearFloats(EClear clear)
{
    positionNewFloats();
    // set y position
    LayoutUnit newY = 0;
    switch (clear) {
    case CLEFT:
        newY = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
        break;
    case CRIGHT:
        newY = lowestFloatLogicalBottom(FloatingObject::FloatRight);
        break;
    case CBOTH:
        newY = lowestFloatLogicalBottom();
    default:
        break;
    }
    if (height() < newY)
        setLogicalHeight(newY);
}

bool RenderBlockFlow::containsFloat(RenderBox* renderer) const
{
    return m_floatingObjects && m_floatingObjects->set().contains<FloatingObjectHashTranslator>(renderer);
}

void RenderBlockFlow::removeFloatingObjects()
{
    if (!m_floatingObjects)
        return;

    markSiblingsWithFloatsForLayout();

    m_floatingObjects->clear();
}

LayoutPoint RenderBlockFlow::flipFloatForWritingModeForChild(const FloatingObject* child, const LayoutPoint& point) const
{
    if (!style()->isFlippedBlocksWritingMode())
        return point;

    // This is similar to RenderBox::flipForWritingModeForChild. We have to subtract out our left/top offsets twice, since
    // it's going to get added back in. We hide this complication here so that the calling code looks normal for the unflipped
    // case.
    if (isHorizontalWritingMode())
        return LayoutPoint(point.x(), point.y() + height() - child->renderer()->height() - 2 * yPositionForFloatIncludingMargin(child));
    return LayoutPoint(point.x() + width() - child->renderer()->width() - 2 * xPositionForFloatIncludingMargin(child), point.y());
}

LayoutUnit RenderBlockFlow::logicalLeftOffsetForPositioningFloat(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit* heightRemaining) const
{
    LayoutUnit offset = fixedOffset;
    if (m_floatingObjects && m_floatingObjects->hasLeftObjects())
        offset = m_floatingObjects->logicalLeftOffsetForPositioningFloat(fixedOffset, logicalTop, heightRemaining);
    return adjustLogicalLeftOffsetForLine(offset, applyTextIndent);
}

LayoutUnit RenderBlockFlow::logicalRightOffsetForPositioningFloat(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit* heightRemaining) const
{
    LayoutUnit offset = fixedOffset;
    if (m_floatingObjects && m_floatingObjects->hasRightObjects())
        offset = m_floatingObjects->logicalRightOffsetForPositioningFloat(fixedOffset, logicalTop, heightRemaining);
    return adjustLogicalRightOffsetForLine(offset, applyTextIndent);
}

LayoutUnit RenderBlockFlow::adjustLogicalLeftOffsetForLine(LayoutUnit offsetFromFloats, bool applyTextIndent) const
{
    LayoutUnit left = offsetFromFloats;

    if (applyTextIndent && style()->isLeftToRightDirection())
        left += textIndentOffset();

    return left;
}

LayoutUnit RenderBlockFlow::adjustLogicalRightOffsetForLine(LayoutUnit offsetFromFloats, bool applyTextIndent) const
{
    LayoutUnit right = offsetFromFloats;

    if (applyTextIndent && !style()->isLeftToRightDirection())
        right -= textIndentOffset();

    return right;
}

LayoutPoint RenderBlockFlow::computeLogicalLocationForFloat(const FloatingObject* floatingObject, LayoutUnit logicalTopOffset) const
{
    RenderBox* childBox = floatingObject->renderer();
    LayoutUnit logicalLeftOffset = logicalLeftOffsetForContent(); // Constant part of left offset.
    LayoutUnit logicalRightOffset; // Constant part of right offset.
    logicalRightOffset = logicalRightOffsetForContent();

    LayoutUnit floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset); // The width we look for.

    LayoutUnit floatLogicalLeft;

    bool insideFlowThread = flowThreadContainingBlock();

    if (childBox->style()->floating() == LeftFloat) {
        LayoutUnit heightRemainingLeft = 1;
        LayoutUnit heightRemainingRight = 1;
        floatLogicalLeft = logicalLeftOffsetForPositioningFloat(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
        while (logicalRightOffsetForPositioningFloat(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight) - floatLogicalLeft < floatLogicalWidth) {
            logicalTopOffset += std::min(heightRemainingLeft, heightRemainingRight);
            floatLogicalLeft = logicalLeftOffsetForPositioningFloat(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
            if (insideFlowThread) {
                // Have to re-evaluate all of our offsets, since they may have changed.
                logicalRightOffset = logicalRightOffsetForContent(); // Constant part of right offset.
                logicalLeftOffset = logicalLeftOffsetForContent(); // Constant part of left offset.
                floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
            }
        }
        floatLogicalLeft = std::max(logicalLeftOffset - borderAndPaddingLogicalLeft(), floatLogicalLeft);
    } else {
        LayoutUnit heightRemainingLeft = 1;
        LayoutUnit heightRemainingRight = 1;
        floatLogicalLeft = logicalRightOffsetForPositioningFloat(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
        while (floatLogicalLeft - logicalLeftOffsetForPositioningFloat(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft) < floatLogicalWidth) {
            logicalTopOffset += std::min(heightRemainingLeft, heightRemainingRight);
            floatLogicalLeft = logicalRightOffsetForPositioningFloat(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
            if (insideFlowThread) {
                // Have to re-evaluate all of our offsets, since they may have changed.
                logicalRightOffset = logicalRightOffsetForContent(); // Constant part of right offset.
                logicalLeftOffset = logicalLeftOffsetForContent(); // Constant part of left offset.
                floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
            }
        }
        // Use the original width of the float here, since the local variable
        // |floatLogicalWidth| was capped to the available line width. See
        // fast/block/float/clamped-right-float.html.
        floatLogicalLeft -= logicalWidthForFloat(floatingObject);
    }

    return LayoutPoint(floatLogicalLeft, logicalTopOffset);
}

FloatingObject* RenderBlockFlow::insertFloatingObject(RenderBox* floatBox)
{
    ASSERT(floatBox->isFloating());

    // Create the list of special objects if we don't aleady have one
    if (!m_floatingObjects) {
        createFloatingObjects();
    } else {
        // Don't insert the object again if it's already in the list
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator it = floatingObjectSet.find<FloatingObjectHashTranslator>(floatBox);
        if (it != floatingObjectSet.end())
            return it->get();
    }

    // Create the special object entry & append it to the list

    OwnPtr<FloatingObject> newObj = FloatingObject::create(floatBox);

    // Our location is irrelevant if we're unsplittable or no pagination is in effect.
    // Just go ahead and lay out the float.
    bool isChildRenderBlock = floatBox->isRenderBlock();
    if (isChildRenderBlock && !floatBox->needsLayout() && view()->layoutState()->pageLogicalHeightChanged())
        floatBox->setChildNeedsLayout(MarkOnlyThis);

    bool needsBlockDirectionLocationSetBeforeLayout = isChildRenderBlock && view()->layoutState()->needsBlockDirectionLocationSetBeforeLayout();
    if (!needsBlockDirectionLocationSetBeforeLayout || isWritingModeRoot()) { // We are unsplittable if we're a block flow root.
        floatBox->layoutIfNeeded();
    } else {
        floatBox->updateLogicalWidth();
        floatBox->computeAndSetBlockDirectionMargins(this);
    }

    setLogicalWidthForFloat(newObj.get(), logicalWidthForChild(floatBox) + marginStartForChild(floatBox) + marginEndForChild(floatBox));

    return m_floatingObjects->add(newObj.release());
}

void RenderBlockFlow::removeFloatingObject(RenderBox* floatBox)
{
    if (m_floatingObjects) {
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator it = floatingObjectSet.find<FloatingObjectHashTranslator>(floatBox);
        if (it != floatingObjectSet.end()) {
            FloatingObject* floatingObject = it->get();
            if (childrenInline()) {
                LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
                LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);

                // Fix for https://bugs.webkit.org/show_bug.cgi?id=54995.
                if (logicalBottom < 0 || logicalBottom < logicalTop || logicalTop == LayoutUnit::max()) {
                    logicalBottom = LayoutUnit::max();
                } else {
                    // Special-case zero- and less-than-zero-height floats: those don't touch
                    // the line that they're on, but it still needs to be dirtied. This is
                    // accomplished by pretending they have a height of 1.
                    logicalBottom = std::max(logicalBottom, logicalTop + 1);
                }
                if (floatingObject->originatingLine()) {
                    if (!selfNeedsLayout()) {
                        ASSERT(floatingObject->originatingLine()->renderer() == this);
                        floatingObject->originatingLine()->markDirty();
                    }
#if ENABLE(ASSERT)
                    floatingObject->setOriginatingLine(0);
#endif
                }
                markLinesDirtyInBlockRange(0, logicalBottom);
            }
            m_floatingObjects->remove(floatingObject);
        }
    }
}

void RenderBlockFlow::removeFloatingObjectsBelow(FloatingObject* lastFloat, int logicalOffset)
{
    if (!containsFloats())
        return;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObject* curr = floatingObjectSet.last().get();
    while (curr != lastFloat && (!curr->isPlaced() || logicalTopForFloat(curr) >= logicalOffset)) {
        m_floatingObjects->remove(curr);
        if (floatingObjectSet.isEmpty())
            break;
        curr = floatingObjectSet.last().get();
    }
}

bool RenderBlockFlow::positionNewFloats()
{
    if (!m_floatingObjects)
        return false;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    if (floatingObjectSet.isEmpty())
        return false;

    // If all floats have already been positioned, then we have no work to do.
    if (floatingObjectSet.last()->isPlaced())
        return false;

    // Move backwards through our floating object list until we find a float that has
    // already been positioned. Then we'll be able to move forward, positioning all of
    // the new floats that need it.
    FloatingObjectSetIterator it = floatingObjectSet.end();
    --it; // Go to last item.
    FloatingObjectSetIterator begin = floatingObjectSet.begin();
    FloatingObject* lastPlacedFloatingObject = 0;
    while (it != begin) {
        --it;
        if ((*it)->isPlaced()) {
            lastPlacedFloatingObject = it->get();
            ++it;
            break;
        }
    }

    LayoutUnit logicalTop = logicalHeight();

    // The float cannot start above the top position of the last positioned float.
    if (lastPlacedFloatingObject)
        logicalTop = std::max(logicalTopForFloat(lastPlacedFloatingObject), logicalTop);

    FloatingObjectSetIterator end = floatingObjectSet.end();
    // Now walk through the set of unpositioned floats and place them.
    for (; it != end; ++it) {
        FloatingObject* floatingObject = it->get();
        // The containing block is responsible for positioning floats, so if we have floats in our
        // list that come from somewhere else, do not attempt to position them.
        if (floatingObject->renderer()->containingBlock() != this)
            continue;

        RenderBox* childBox = floatingObject->renderer();

        // FIXME Investigate if this can be removed. crbug.com/370006
        childBox->setMayNeedPaintInvalidation(true);

        LayoutUnit childLogicalLeftMargin = style()->isLeftToRightDirection() ? marginStartForChild(childBox) : marginEndForChild(childBox);
        if (childBox->style()->clear() & CLEFT)
            logicalTop = std::max(lowestFloatLogicalBottom(FloatingObject::FloatLeft), logicalTop);
        if (childBox->style()->clear() & CRIGHT)
            logicalTop = std::max(lowestFloatLogicalBottom(FloatingObject::FloatRight), logicalTop);

        LayoutPoint floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, logicalTop);

        setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

        setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
        setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));

        SubtreeLayoutScope layoutScope(*childBox);
        LayoutState* layoutState = view()->layoutState();
        bool isPaginated = layoutState->isPaginated();
        if (isPaginated && !childBox->needsLayout())
            childBox->markForPaginationRelayoutIfNeeded(layoutScope);

        childBox->layoutIfNeeded();

        if (isPaginated) {
            // If we are unsplittable and don't fit, then we need to move down.
            // We include our margins as part of the unsplittable area.
            LayoutUnit newLogicalTop = adjustForUnsplittableChild(childBox, floatLogicalLocation.y(), true);

            // See if we have a pagination strut that is making us move down further.
            // Note that an unsplittable child can't also have a pagination strut, so this is
            // exclusive with the case above.
            RenderBlockFlow* childBlockFlow = childBox->isRenderBlockFlow() ? toRenderBlockFlow(childBox) : 0;
            if (childBlockFlow && childBlockFlow->paginationStrut()) {
                newLogicalTop += childBlockFlow->paginationStrut();
                childBlockFlow->setPaginationStrut(0);
            }

            if (newLogicalTop != floatLogicalLocation.y()) {
                floatingObject->setPaginationStrut(newLogicalTop - floatLogicalLocation.y());

                floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, newLogicalTop);
                setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

                setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
                setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));

                if (childBox->isRenderBlock())
                    childBox->setChildNeedsLayout(MarkOnlyThis);
                childBox->layoutIfNeeded();
            }
        }

        setLogicalTopForFloat(floatingObject, floatLogicalLocation.y());

        setLogicalHeightForFloat(floatingObject, logicalHeightForChild(childBox) + marginBeforeForChild(childBox) + marginAfterForChild(childBox));

        m_floatingObjects->addPlacedObject(floatingObject);

        if (ShapeOutsideInfo* shapeOutside = childBox->shapeOutsideInfo())
            shapeOutside->setReferenceBoxLogicalSize(logicalSizeForChild(childBox));
    }
    return true;
}

bool RenderBlockFlow::hasOverhangingFloat(RenderBox* renderer)
{
    if (!m_floatingObjects || hasColumns() || !parent())
        return false;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator it = floatingObjectSet.find<FloatingObjectHashTranslator>(renderer);
    if (it == floatingObjectSet.end())
        return false;

    return logicalBottomForFloat(it->get()) > logicalHeight();
}

void RenderBlockFlow::addIntrudingFloats(RenderBlockFlow* prev, LayoutUnit logicalLeftOffset, LayoutUnit logicalTopOffset)
{
    ASSERT(!avoidsFloats());

    // If we create our own block formatting context then our contents don't interact with floats outside it, even those from our parent.
    if (createsBlockFormattingContext())
        return;

    // If the parent or previous sibling doesn't have any floats to add, don't bother.
    if (!prev->m_floatingObjects)
        return;

    logicalLeftOffset += marginLogicalLeft();

    const FloatingObjectSet& prevSet = prev->m_floatingObjects->set();
    FloatingObjectSetIterator prevEnd = prevSet.end();
    for (FloatingObjectSetIterator prevIt = prevSet.begin(); prevIt != prevEnd; ++prevIt) {
        FloatingObject* floatingObject = prevIt->get();
        if (logicalBottomForFloat(floatingObject) > logicalTopOffset) {
            if (!m_floatingObjects || !m_floatingObjects->set().contains(floatingObject)) {
                // We create the floating object list lazily.
                if (!m_floatingObjects)
                    createFloatingObjects();

                // Applying the child's margin makes no sense in the case where the child was passed in.
                // since this margin was added already through the modification of the |logicalLeftOffset| variable
                // above. |logicalLeftOffset| will equal the margin in this case, so it's already been taken
                // into account. Only apply this code if prev is the parent, since otherwise the left margin
                // will get applied twice.
                LayoutSize offset = isHorizontalWritingMode()
                    ? LayoutSize(logicalLeftOffset - (prev != parent() ? prev->marginLeft() : LayoutUnit()), logicalTopOffset)
                    : LayoutSize(logicalTopOffset, logicalLeftOffset - (prev != parent() ? prev->marginTop() : LayoutUnit()));

                m_floatingObjects->add(floatingObject->copyToNewContainer(offset));
            }
        }
    }
}

void RenderBlockFlow::addOverhangingFloats(RenderBlockFlow* child, bool makeChildPaintOtherFloats)
{
    // Prevent floats from being added to the canvas by the root element, e.g., <html>.
    if (!child->containsFloats() || child->isRenderRegion() || child->createsBlockFormattingContext())
        return;

    LayoutUnit childLogicalTop = child->logicalTop();
    LayoutUnit childLogicalLeft = child->logicalLeft();

    // Floats that will remain the child's responsibility to paint should factor into its
    // overflow.
    FloatingObjectSetIterator childEnd = child->m_floatingObjects->set().end();
    for (FloatingObjectSetIterator childIt = child->m_floatingObjects->set().begin(); childIt != childEnd; ++childIt) {
        FloatingObject* floatingObject = childIt->get();
        LayoutUnit logicalBottomForFloat = std::min(this->logicalBottomForFloat(floatingObject), LayoutUnit::max() - childLogicalTop);
        LayoutUnit logicalBottom = childLogicalTop + logicalBottomForFloat;

        if (logicalBottom > logicalHeight()) {
            // If the object is not in the list, we add it now.
            if (!containsFloat(floatingObject->renderer())) {
                LayoutSize offset = isHorizontalWritingMode() ? LayoutSize(-childLogicalLeft, -childLogicalTop) : LayoutSize(-childLogicalTop, -childLogicalLeft);
                bool shouldPaint = false;

                // The nearest enclosing layer always paints the float (so that zindex and stacking
                // behaves properly). We always want to propagate the desire to paint the float as
                // far out as we can, to the outermost block that overlaps the float, stopping only
                // if we hit a self-painting layer boundary.
                if (floatingObject->renderer()->enclosingFloatPaintingLayer() == enclosingFloatPaintingLayer()) {
                    floatingObject->setShouldPaint(false);
                    shouldPaint = true;
                }
                // We create the floating object list lazily.
                if (!m_floatingObjects)
                    createFloatingObjects();

                m_floatingObjects->add(floatingObject->copyToNewContainer(offset, shouldPaint, true));
            }
        } else {
            if (makeChildPaintOtherFloats && !floatingObject->shouldPaint() && !floatingObject->renderer()->hasSelfPaintingLayer()
                && floatingObject->renderer()->isDescendantOf(child) && floatingObject->renderer()->enclosingFloatPaintingLayer() == child->enclosingFloatPaintingLayer()) {
                // The float is not overhanging from this block, so if it is a descendant of the child, the child should
                // paint it (the other case is that it is intruding into the child), unless it has its own layer or enclosing
                // layer.
                // If makeChildPaintOtherFloats is false, it means that the child must already know about all the floats
                // it should paint.
                floatingObject->setShouldPaint(true);
            }

            // Since the float doesn't overhang, it didn't get put into our list. We need to go ahead and add its overflow in to the
            // child now.
            if (floatingObject->isDescendant())
                child->addOverflowFromChild(floatingObject->renderer(), LayoutSize(xPositionForFloatIncludingMargin(floatingObject), yPositionForFloatIncludingMargin(floatingObject)));
        }
    }
}

LayoutUnit RenderBlockFlow::lowestFloatLogicalBottom(FloatingObject::Type floatType) const
{
    if (!m_floatingObjects)
        return 0;

    return m_floatingObjects->lowestFloatLogicalBottom(floatType);
}

LayoutUnit RenderBlockFlow::nextFloatLogicalBottomBelow(LayoutUnit logicalHeight, ShapeOutsideFloatOffsetMode offsetMode) const
{
    if (!m_floatingObjects)
        return logicalHeight;

    LayoutUnit logicalBottom;
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* floatingObject = it->get();
        LayoutUnit floatLogicalBottom = logicalBottomForFloat(floatingObject);
        ShapeOutsideInfo* shapeOutside = floatingObject->renderer()->shapeOutsideInfo();
        if (shapeOutside && (offsetMode == ShapeOutsideFloatShapeOffset)) {
            LayoutUnit shapeLogicalBottom = logicalTopForFloat(floatingObject) + marginBeforeForChild(floatingObject->renderer()) + shapeOutside->shapeLogicalBottom();
            // Use the shapeLogicalBottom unless it extends outside of the margin box, in which case it is clipped.
            if (shapeLogicalBottom < floatLogicalBottom)
                floatLogicalBottom = shapeLogicalBottom;
        }
        if (floatLogicalBottom > logicalHeight)
            logicalBottom = logicalBottom ? std::min(floatLogicalBottom, logicalBottom) : floatLogicalBottom;
    }

    return logicalBottom;
}

bool RenderBlockFlow::hitTestFloats(const HitTestRequest& request, HitTestResult& result, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset)
{
    if (!m_floatingObjects)
        return false;

    LayoutPoint adjustedLocation = accumulatedOffset;
    if (isRenderView()) {
        adjustedLocation += toLayoutSize(toRenderView(this)->frameView()->scrollPosition());
    }

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator begin = floatingObjectSet.begin();
    for (FloatingObjectSetIterator it = floatingObjectSet.end(); it != begin;) {
        --it;
        FloatingObject* floatingObject = it->get();
        if (floatingObject->shouldPaint() && !floatingObject->renderer()->hasSelfPaintingLayer()) {
            LayoutUnit xOffset = xPositionForFloatIncludingMargin(floatingObject) - floatingObject->renderer()->x();
            LayoutUnit yOffset = yPositionForFloatIncludingMargin(floatingObject) - floatingObject->renderer()->y();
            LayoutPoint childPoint = flipFloatForWritingModeForChild(floatingObject, adjustedLocation + LayoutSize(xOffset, yOffset));
            if (floatingObject->renderer()->hitTest(request, result, locationInContainer, childPoint)) {
                updateHitTestResult(result, locationInContainer.point() - toLayoutSize(childPoint));
                return true;
            }
        }
    }

    return false;
}

void RenderBlockFlow::adjustForBorderFit(LayoutUnit x, LayoutUnit& left, LayoutUnit& right) const
{
    if (style()->visibility() != VISIBLE)
        return;

    // We don't deal with relative positioning. Our assumption is that you shrink to fit the lines without accounting
    // for either overflow or translations via relative positioning.
    if (childrenInline()) {
        for (RootInlineBox* box = firstRootBox(); box; box = box->nextRootBox()) {
            if (box->firstChild())
                left = std::min(left, x + static_cast<LayoutUnit>(box->firstChild()->x()));
            if (box->lastChild())
                right = std::max(right, x + static_cast<LayoutUnit>(ceilf(box->lastChild()->logicalRight())));
        }
    } else {
        for (RenderBox* obj = firstChildBox(); obj; obj = obj->nextSiblingBox()) {
            if (!obj->isFloatingOrOutOfFlowPositioned()) {
                if (obj->isRenderBlockFlow() && !obj->hasOverflowClip()) {
                    toRenderBlockFlow(obj)->adjustForBorderFit(x + obj->x(), left, right);
                } else if (obj->style()->visibility() == VISIBLE) {
                    // We are a replaced element or some kind of non-block-flow object.
                    left = std::min(left, x + obj->x());
                    right = std::max(right, x + obj->x() + obj->width());
                }
            }
        }
    }

    if (m_floatingObjects) {
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator end = floatingObjectSet.end();
        for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
            FloatingObject* floatingObject = it->get();
            // Only examine the object if our m_shouldPaint flag is set.
            if (floatingObject->shouldPaint()) {
                LayoutUnit floatLeft = xPositionForFloatIncludingMargin(floatingObject) - floatingObject->renderer()->x();
                LayoutUnit floatRight = floatLeft + floatingObject->renderer()->width();
                left = std::min(left, floatLeft);
                right = std::max(right, floatRight);
            }
        }
    }
}

void RenderBlockFlow::fitBorderToLinesIfNeeded()
{
    if (style()->borderFit() == BorderFitBorder || hasOverrideWidth())
        return;

    // Walk any normal flow lines to snugly fit.
    LayoutUnit left = LayoutUnit::max();
    LayoutUnit right = LayoutUnit::min();
    LayoutUnit oldWidth = contentWidth();
    adjustForBorderFit(0, left, right);

    // Clamp to our existing edges. We can never grow. We only shrink.
    LayoutUnit leftEdge = borderLeft() + paddingLeft();
    LayoutUnit rightEdge = leftEdge + oldWidth;
    left = std::min(rightEdge, std::max(leftEdge, left));
    right = std::max(left, std::min(rightEdge, right));

    LayoutUnit newContentWidth = right - left;
    if (newContentWidth == oldWidth)
        return;

    setOverrideLogicalContentWidth(newContentWidth);
    layoutBlock(false);
    clearOverrideLogicalContentWidth();
}

LayoutUnit RenderBlockFlow::logicalLeftFloatOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, LayoutUnit logicalHeight) const
{
    if (m_floatingObjects && m_floatingObjects->hasLeftObjects())
        return m_floatingObjects->logicalLeftOffset(fixedOffset, logicalTop, logicalHeight);

    return fixedOffset;
}

LayoutUnit RenderBlockFlow::logicalRightFloatOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, LayoutUnit logicalHeight) const
{
    if (m_floatingObjects && m_floatingObjects->hasRightObjects())
        return m_floatingObjects->logicalRightOffset(fixedOffset, logicalTop, logicalHeight);

    return fixedOffset;
}

GapRects RenderBlockFlow::inlineSelectionGaps(const RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
    LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const PaintInfo* paintInfo) const
{
    GapRects result;

    bool containsStart = selectionState() == SelectionStart || selectionState() == SelectionBoth;

    if (!firstLineBox()) {
        if (containsStart) {
            // Go ahead and update our lastLogicalTop to be the bottom of the block.  <hr>s or empty blocks with height can trip this
            // case.
            lastLogicalTop = rootBlock->blockDirectionOffset(offsetFromRootBlock) + logicalHeight();
            lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, logicalHeight());
            lastLogicalRight = logicalRightSelectionOffset(rootBlock, logicalHeight());
        }
        return result;
    }

    RootInlineBox* lastSelectedLine = 0;
    RootInlineBox* curr;
    for (curr = firstRootBox(); curr && !curr->hasSelectedChildren(); curr = curr->nextRootBox()) { }

    // Now paint the gaps for the lines.
    for (; curr && curr->hasSelectedChildren(); curr = curr->nextRootBox()) {
        LayoutUnit selTop =  curr->selectionTopAdjustedForPrecedingBlock();
        LayoutUnit selHeight = curr->selectionHeightAdjustedForPrecedingBlock();

        if (!containsStart && !lastSelectedLine && selectionState() != SelectionStart && selectionState() != SelectionBoth) {
            result.uniteCenter(blockSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop,
                lastLogicalLeft, lastLogicalRight, selTop, paintInfo));
        }

        LayoutRect logicalRect(curr->logicalLeft(), selTop, curr->logicalWidth(), selTop + selHeight);
        logicalRect.move(isHorizontalWritingMode() ? offsetFromRootBlock : offsetFromRootBlock.transposedSize());
        LayoutRect physicalRect = rootBlock->logicalRectToPhysicalRect(rootBlockPhysicalPosition, logicalRect);
        if (!paintInfo || (isHorizontalWritingMode() && physicalRect.y() < paintInfo->rect.maxY() && physicalRect.maxY() > paintInfo->rect.y())
            || (!isHorizontalWritingMode() && physicalRect.x() < paintInfo->rect.maxX() && physicalRect.maxX() > paintInfo->rect.x()))
            result.unite(curr->lineSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, selTop, selHeight, paintInfo));

        lastSelectedLine = curr;
    }

    if (containsStart && !lastSelectedLine) {
        // VisibleSelection must start just after our last line.
        lastSelectedLine = lastRootBox();
    }

    if (lastSelectedLine && selectionState() != SelectionEnd && selectionState() != SelectionBoth) {
        // Go ahead and update our lastY to be the bottom of the last selected line.
        lastLogicalTop = rootBlock->blockDirectionOffset(offsetFromRootBlock) + lastSelectedLine->selectionBottom();
        lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, lastSelectedLine->selectionBottom());
        lastLogicalRight = logicalRightSelectionOffset(rootBlock, lastSelectedLine->selectionBottom());
    }
    return result;
}

void RenderBlockFlow::setPaginationStrut(LayoutUnit strut)
{
    if (!m_rareData) {
        if (!strut)
            return;
        m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
    }
    m_rareData->m_paginationStrut = strut;
}

bool RenderBlockFlow::avoidsFloats() const
{
    // Floats can't intrude into our box if we have a non-auto column count or width.
    // Note: we need to use RenderBox::avoidsFloats here since RenderBlock::avoidsFloats is always true.
    return RenderBox::avoidsFloats() || !style()->hasAutoColumnCount() || !style()->hasAutoColumnWidth();
}

LayoutUnit RenderBlockFlow::logicalLeftSelectionOffset(const RenderBlock* rootBlock, LayoutUnit position) const
{
    LayoutUnit logicalLeft = logicalLeftOffsetForLine(position, false);
    if (logicalLeft == logicalLeftOffsetForContent())
        return RenderBlock::logicalLeftSelectionOffset(rootBlock, position);

    const RenderBlock* cb = this;
    while (cb != rootBlock) {
        logicalLeft += cb->logicalLeft();
        cb = cb->containingBlock();
    }
    return logicalLeft;
}

LayoutUnit RenderBlockFlow::logicalRightSelectionOffset(const RenderBlock* rootBlock, LayoutUnit position) const
{
    LayoutUnit logicalRight = logicalRightOffsetForLine(position, false);
    if (logicalRight == logicalRightOffsetForContent())
        return RenderBlock::logicalRightSelectionOffset(rootBlock, position);

    const RenderBlock* cb = this;
    while (cb != rootBlock) {
        logicalRight += cb->logicalLeft();
        cb = cb->containingBlock();
    }
    return logicalRight;
}

RootInlineBox* RenderBlockFlow::createRootInlineBox()
{
    return new RootInlineBox(*this);
}

bool RenderBlockFlow::isPagedOverflow(const RenderStyle* style)
{
    return style->isOverflowPaged() && node() != document().viewportDefiningElement();
}

RenderBlockFlow::FlowThreadType RenderBlockFlow::flowThreadType(const RenderStyle* style)
{
    if (isPagedOverflow(style))
        return PagedFlowThread;
    if (style->specifiesColumns())
        return MultiColumnFlowThread;
    return NoFlowThread;
}

RenderMultiColumnFlowThread* RenderBlockFlow::createMultiColumnFlowThread(FlowThreadType type)
{
    switch (type) {
    case MultiColumnFlowThread:
        return RenderMultiColumnFlowThread::createAnonymous(document(), style());
    case PagedFlowThread:
        // Paged overflow is currently done using the multicol implementation.
        return RenderPagedFlowThread::createAnonymous(document(), style());
    default:
        ASSERT_NOT_REACHED();
        return nullptr;
    }
}

void RenderBlockFlow::createOrDestroyMultiColumnFlowThreadIfNeeded(const RenderStyle* oldStyle)
{
    if (!document().regionBasedColumnsEnabled())
        return;

    // Paged overflow trumps multicol in this implementation. Ideally, it should be possible to have
    // both paged overflow and multicol on the same element, but then we need two flow
    // threads. Anyway, this is nothing to worry about until we can actually nest multicol properly
    // inside other fragmentation contexts.
    FlowThreadType type = flowThreadType(style());

    if (multiColumnFlowThread()) {
        ASSERT(oldStyle);
        if (type != flowThreadType(oldStyle)) {
            // If we're no longer to be multicol/paged, destroy the flow thread. Also destroy it
            // when switching between multicol and paged, since that affects the column set
            // structure (multicol containers may have spanners, paged containers may not).
            multiColumnFlowThread()->evacuateAndDestroy();
            ASSERT(!multiColumnFlowThread());
        }
    }

    if (type == NoFlowThread || multiColumnFlowThread())
        return;

    RenderMultiColumnFlowThread* flowThread = createMultiColumnFlowThread(type);
    addChild(flowThread);
    flowThread->populate();
    RenderBlockFlowRareData& rareData = ensureRareData();
    ASSERT(!rareData.m_multiColumnFlowThread);
    rareData.m_multiColumnFlowThread = flowThread;
}

RenderBlockFlow::RenderBlockFlowRareData& RenderBlockFlow::ensureRareData()
{
    if (m_rareData)
        return *m_rareData;

    m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
    return *m_rareData;
}

void RenderBlockFlow::positionDialog()
{
    HTMLDialogElement* dialog = toHTMLDialogElement(node());
    if (dialog->centeringMode() == HTMLDialogElement::NotCentered)
        return;

    bool canCenterDialog = (style()->position() == AbsolutePosition || style()->position() == FixedPosition)
        && style()->hasAutoTopAndBottom();

    if (dialog->centeringMode() == HTMLDialogElement::Centered) {
        if (canCenterDialog)
            setY(dialog->centeredPosition());
        return;
    }

    ASSERT(dialog->centeringMode() == HTMLDialogElement::NeedsCentering);
    if (!canCenterDialog) {
        dialog->setNotCentered();
        return;
    }

    FrameView* frameView = document().view();
    LayoutUnit top = (style()->position() == FixedPosition) ? 0 : frameView->scrollOffset().height();
    int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
    if (height() < visibleHeight)
        top += (visibleHeight - height()) / 2;
    setY(top);
    dialog->setCentered(top);
}

} // namespace blink