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

Source/core/rendering/RenderLayerModelObject.h

Index: Source/core/rendering/RenderLayerModelObject.h
diff --git a/Source/core/rendering/RenderLayerModelObject.h b/Source/core/rendering/RenderLayerModelObject.h
index 559c4ea8d0cf0dc164b50cebe6840eca7d5c6ea6..947509dd85cac3cbc2a1ad3db08cab124ac30d5c 100644
--- a/Source/core/rendering/RenderLayerModelObject.h
+++ b/Source/core/rendering/RenderLayerModelObject.h
@@ -23,6 +23,7 @@
 #ifndef RenderLayerModelObject_h
 #define RenderLayerModelObject_h
 
+#include "core/rendering/CompositedLayerMappingPtr.h"
 #include "core/rendering/RenderObject.h"
 
 namespace WebCore {
@@ -56,7 +57,7 @@ public:
     // This is null for anonymous renderers.
     ContainerNode* node() const { return toContainerNode(RenderObject::node()); }
 
-    CompositedLayerMapping* compositedLayerMapping() const;
+    CompositedLayerMappingPtr compositedLayerMapping() const;
 
 protected:
     void createLayer();