Don't coerce pointers to compositor layer mappings to booleans.

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 1239 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())
         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 516 matching lines @@
     }
 
     document->updateLayout();
 
     RenderView* view = document->renderView();
     if (view->compositor())
         view->compositor()->updateCompositingLayers(CompositingUpdateFinishAllDeferredWork);
 }
 
 }