Clear box from percentage descendants when it is split off from the ancestor

third_party/WebKit/Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 4676 matching lines @@
             // We need to invalidate the |parentBox| before inserting the new node
             // so that the table paint invalidation logic knows the structure is dirty.
             // See for example LayoutTableCell:clippedOverflowRectForPaintInvalidation.
             markBoxForRelayoutAfterSplit(parentBox);
             parentBox->virtualChildren()->insertChildNode(parentBox, postBox, boxToSplit->nextSibling());
             boxToSplit->moveChildrenTo(postBox, beforeChild, 0, true);
 
             markBoxForRelayoutAfterSplit(boxToSplit);
             markBoxForRelayoutAfterSplit(postBox);
 
+            // Splitting the box means the left side of the container chain will lose any percent height descendants
+            // below |postBox| in the right hand side.
+            if (LayoutBlock::hasPercentHeightContainerMap())
+                LayoutBlock::clearPercentHeightDescendantsFrom(postBox);

[mstensho (USE GERRIT), 2016/01/25 09:17:07]

This will process the entire postBox subtree, which could be expensive. But I
assume this is the only safe thing to do?

We could at least avoid some work if we only do this only *once* per
splitAnonymousBoxesAroundChild() call, i.e. do it on the topmost postBox that we
create.

[rhogan, 2016/01/25 19:14:55]

:$

Updated this and the test. Thanks.

+
             beforeChild = postBox;
         } else {
             beforeChild = boxToSplit;
         }
     }
 
     if (didSplitParentAnonymousBoxes)
         markBoxForRelayoutAfterSplit(this);
 
     ASSERT(beforeChild->parent() == this);
@@ skipping 197 matching lines @@
 }
 
 void LayoutBox::clearPreviousPaintInvalidationRects()
 {
     LayoutBoxModelObject::clearPreviousPaintInvalidationRects();
     if (PaintLayerScrollableArea* scrollableArea = this->scrollableArea())
         scrollableArea->clearPreviousPaintInvalidationRects();
 }
 
 } // namespace blink