Use a boolean hasCompositedLayerMapping() accessor instead of the pointer

Source/core/testing/Internals.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple 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.
@@ skipping 1252 matching lines @@
         return 0;
 
     unsigned count = 0;
     for (TouchEventTargetSet::const_iterator iter = touchHandlers->begin(); iter != touchHandlers->end(); ++iter)
         count += iter->value;
     return count;
 }
 
 static RenderLayer* findRenderLayerForGraphicsLayer(RenderLayer* searchRoot, GraphicsLayer* graphicsLayer, String* layerType)
 {
-    if (searchRoot->compositedLayerMapping() && graphicsLayer == searchRoot->compositedLayerMapping()->mainGraphicsLayer())
+    // Note, we only want to return the RenderLayer that _truly_ owns the GraphicsLayer, not just the
+    // first RenderLayer we encounter that paints into it.
+    if (searchRoot->compositingState() == PaintsIntoOwnBacking && graphicsLayer == searchRoot->compositedLayerMapping()->mainGraphicsLayer())

[shawnsingh, 2013/11/12 21:12:50]

Option 1: maybe we should keep this as hasCompositedLayerMapping for now

Option 2: can you please explain why it should not be true when
HasOwnBackingButPaintsIntoAncestor?  based on the comment, it should include
that condition.  the mainGraphicsLayer will still exist for composited
RenderLayers that paint into ancestor.

         return searchRoot;
 
     GraphicsLayer* layerForScrolling = searchRoot->scrollableArea() ? searchRoot->scrollableArea()->layerForScrolling() : 0;
     if (graphicsLayer == layerForScrolling) {
         *layerType = "scrolling";
         return searchRoot;
     }
 
     GraphicsLayer* layerForHorizontalScrollbar = searchRoot->scrollableArea() ? searchRoot->scrollableArea()->layerForHorizontalScrollbar() : 0;
     if (graphicsLayer == layerForHorizontalScrollbar) {
@@ skipping 462 matching lines @@
     element->document().updateLayout();
 
     RenderObject* renderer = element->renderer();
     if (!renderer || !renderer->isBox()) {
         es.throwUninformativeAndGenericDOMException(InvalidAccessError);
         return String();
     }
 
     RenderLayer* layer = toRenderBox(renderer)->layer();
     if (!layer
-        || !layer->compositedLayerMapping()
+        || !layer->hasCompositedLayerMapping()
         || !layer->compositedLayerMapping()->mainGraphicsLayer()) {
         // Don't raise exception in these cases which may be normally used in tests.
         return String();
     }
 
     return layer->compositedLayerMapping()->mainGraphicsLayer()->layerTreeAsText(flags);
 }
 
 static RenderLayer* getRenderLayerForElement(Element* element, ExceptionState& es)
 {
@@ skipping 494 matching lines @@
     }
 
     document->updateLayout();
 
     RenderView* view = document->renderView();
     if (view->compositor())
         view->compositor()->updateCompositingLayers(CompositingUpdateFinishAllDeferredWork);
 }
 
 }