Return the enclosing composited PaintLayer rather than containingBlock for floats.

third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 39 matching lines @@
       m_compositingAncestor = &layer;
       if (layer.stackingNode()->isStackingContext())
         m_compositingStackingContext = &layer;
     }
   }
 
   const PaintLayer* compositingContainer(const PaintLayer& layer) const {
     // TODO(chrishtr) this is not very performant for floats, but they should
     // be uncommon enough, and SPv2 will remove this code.
     if (layer.layoutObject()->isFloating() && layer.layoutObject()->parent() &&
-        !layer.layoutObject()->parent()->isLayoutBlockFlow())
-      return layer.layoutObject()->containingBlock()->enclosingLayer();
+        !layer.layoutObject()->parent()->isLayoutBlockFlow()) {
+      return layer.enclosingLayerWithCompositedLayerMapping(ExcludeSelf);
+    }
     return layer.stackingNode()->isStacked() ? m_compositingStackingContext
                                              : m_compositingAncestor;
   }
 
   const PaintLayer* compositingStackingContext() const {
     return m_compositingStackingContext;
   }
 
  private:
   const PaintLayer* m_compositingStackingContext;
@@ skipping 56 matching lines @@
         ->assertNeedsToUpdateGraphicsLayerBitsCleared();
 
   for (PaintLayer* child = layer.firstChild(); child;
        child = child->nextSibling())
     assertNeedsToUpdateGraphicsLayerBitsCleared(*child);
 }
 
 #endif
 
 }  // namespace blink