Ensure that positioned objects' list is always in parent first order

Source/core/layout/LayoutBlock.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 263 matching lines @@
     setReplaced(newStyle.isDisplayInlineType());
 
     if (oldStyle && parent()) {
         bool oldStyleIsContainer = oldStyle->position() != StaticPosition || oldStyle->hasTransformRelatedProperty();
         bool newStyleIsContainer = newStyle.position() != StaticPosition || newStyle.hasTransformRelatedProperty();
 
         if (oldStyleIsContainer && !newStyleIsContainer) {
             // Clear our positioned objects list. Our absolutely positioned descendants will be
             // inserted into our containing block's positioned objects list during layout.
             removePositionedObjects(0, NewContainingBlock);
-        } else if (!oldStyleIsContainer && newStyleIsContainer) {
+        } else if ((!oldStyleIsContainer || oldStyle->position() != newStyle.position()) && newStyleIsContainer) {
             // Remove our absolutely positioned descendants from their current containing block.

[mstensho (USE GERRIT), 2015/06/15 10:02:55]

This comment is now inaccurate. We're removing positioned descendants from the
*new* containing block.

             // They will be inserted into our positioned objects list during layout.
-            LayoutObject* cb = parent();
-            while (cb && (cb->style()->position() == StaticPosition || (cb->isInline() && !cb->isReplaced())) && !cb->isLayoutView()) {
-                if (cb->style()->position() == RelativePosition && cb->isInline() && !cb->isReplaced()) {
-                    cb = cb->containingBlock();
-                    break;
-                }
-                cb = cb->parent();
-            }
-
-            if (cb->isLayoutBlock())
-                toLayoutBlock(cb)->removePositionedObjects(this, NewContainingBlock);
+            if (LayoutBlock* cb = containingBlock(&newStyle))

[mstensho (USE GERRIT), 2015/06/15 10:02:54]

Why not do this in styleDidChange() instead of styleWillChange? Then we wouldn't
need the optional overrideStyle parameter to containingBlock().

The entire code block with the oldStyleIsContainer and newStyleIsContainer stuff
could be moved there.

+                cb->removePositionedObjects(this, NewContainingBlock);
         }
     }
 
     LayoutBox::styleWillChange(diff, newStyle);
 }
 
 static bool borderOrPaddingLogicalWidthChanged(const ComputedStyle& oldStyle, const ComputedStyle& newStyle)
 {
     if (newStyle.isHorizontalWritingMode()) {
         return oldStyle.borderLeftWidth() != newStyle.borderLeftWidth()
@@ skipping 2599 matching lines @@
 void LayoutBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const LayoutObject* obj) const
 {
     showLayoutObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace blink