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

Source/core/inspector/InspectorLayerTreeAgent.cpp

Index: Source/core/inspector/InspectorLayerTreeAgent.cpp
diff --git a/Source/core/inspector/InspectorLayerTreeAgent.cpp b/Source/core/inspector/InspectorLayerTreeAgent.cpp
index 5f4df0d79a3582e0b3aacde1c19de3125c906436..609e35e89342f27848c6d3e2915b1661b38b7153 100644
--- a/Source/core/inspector/InspectorLayerTreeAgent.cpp
+++ b/Source/core/inspector/InspectorLayerTreeAgent.cpp
@@ -152,11 +152,10 @@ void InspectorLayerTreeAgent::layerTreeDidChange()
 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())
@@ -179,7 +178,7 @@ PassRefPtr<TypeBuilder::Array<TypeBuilder::LayerTree::Layer> > InspectorLayerTre
 
 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));