Same-document navigation in onload triggered by back navigation.

1. Start the layout test web server with Tools/Scripts/run-webkit-httpd.
2. Click here.
3. Click Back.

You should not crash.

We cannot use history.back() to test this, because it calls Page::goToItem (which calls FrameLoader::stopAllLoaders) first. Chromium's back button does not call stopAllLoaders first.