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

Source/core/inspector/InspectorLayerTreeAgent.cpp

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 134 matching lines @@
 }
 
 void InspectorLayerTreeAgent::layerTreeDidChange()
 {
     m_frontend->layerTreeDidChange(buildLayerTree());
 }
 
 void InspectorLayerTreeAgent::didPaint(RenderObject* renderer, GraphicsContext*, const LayoutRect& rect)
 {
     RenderLayer* renderLayer = toRenderLayerModelObject(renderer)->layer();
-    CompositedLayerMapping* compositedLayerMapping = renderLayer->compositedLayerMapping();
     // Should only happen for FrameView paints when compositing is off. Consider different instrumentation method for that.
-    if (!compositedLayerMapping)
+    if (renderLayer->compositingState() != PaintsIntoOwnBacking)

[shawnsingh, 2013/11/05 10:20:27]

It makes sense if this would never be called when
HasOwnBackingButPaintsIntoAncestor ... but I wouldn't be surprised if this gets
called in that scenario, either.  Do you know for certain what happens here?

[Ian Vollick, 2013/11/08 03:35:12]

Yep, I'm pretty certain. I've updated the code with a comment and added an
ASSERT.

         return;
-    GraphicsLayer* graphicsLayer = compositedLayerMapping->mainGraphicsLayer();
+    GraphicsLayer* graphicsLayer = renderLayer->compositedLayerMapping()->mainGraphicsLayer();
     RefPtr<TypeBuilder::DOM::Rect> domRect = TypeBuilder::DOM::Rect::create()
         .setX(rect.x())
         .setY(rect.y())
         .setWidth(rect.width())
         .setHeight(rect.height());
     m_frontend->layerPainted(idForLayer(graphicsLayer), domRect.release());
 }
 
 PassRefPtr<TypeBuilder::Array<TypeBuilder::LayerTree::Layer> > InspectorLayerTreeAgent::buildLayerTree()
 {
     RenderLayerCompositor* compositor = renderLayerCompositor();
     if (!compositor || !compositor->inCompositingMode())
         return 0;
     LayerIdToNodeIdMap layerIdToNodeIdMap;
     RefPtr<TypeBuilder::Array<TypeBuilder::LayerTree::Layer> > layers = TypeBuilder::Array<TypeBuilder::LayerTree::Layer>::create();
     buildLayerIdToNodeIdMap(compositor->rootRenderLayer(), layerIdToNodeIdMap);
     gatherGraphicsLayers(compositor->rootGraphicsLayer(), layerIdToNodeIdMap, layers);
     return layers.release();
 }
 
 void InspectorLayerTreeAgent::buildLayerIdToNodeIdMap(RenderLayer* root, LayerIdToNodeIdMap& layerIdToNodeIdMap)
 {
-    if (root->compositedLayerMapping()) {
+    if (root->compositingState() == PaintsIntoOwnBacking) {

[shawnsingh, 2013/11/05 10:20:27]

I don't think this one is correct.  The previous code could also have had "true"
for the condition where compositingState() == HasOwnBackingButPaintsIntoAncestor

[Ian Vollick, 2013/11/08 03:35:12]

I think there may have been a bug in the old code. I've added my rationale as a
comment in the code.

         if (Node* node = root->renderer()->generatingNode()) {
             GraphicsLayer* graphicsLayer = root->compositedLayerMapping()->childForSuperlayers();
             layerIdToNodeIdMap.set(graphicsLayer->platformLayer()->id(), idForNode(node));
         }
     }
     for (RenderLayer* child = root->firstChild(); child; child = child->nextSibling())
         buildLayerIdToNodeIdMap(child, layerIdToNodeIdMap);
     if (!root->renderer()->isRenderIFrame())
         return;
     FrameView* childFrameView = toFrameView(toRenderWidget(root->renderer())->widget());
@@ skipping 105 matching lines @@
             continue;
         reasonStrings->addItem(compositingReasonNames[i].protocolName);
 #ifndef _NDEBUG
         reasonsBitmask &= ~compositingReasonNames[i].mask;
 #endif
     }
     ASSERT(!reasonsBitmask);
 }
 
 } // namespace WebCore