Use a boolean hasCompositedLayerMapping() accessor instead of the pointer

Source/core/rendering/RenderLayerModelObject.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010, 2012 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 38 matching lines @@
 
     virtual bool requiresLayer() const = 0;
 
     // Returns true if the background is painted opaque in the given rect.
     // The query rect is given in local coordinate system.
     virtual bool backgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const { return false; }
 
     // This is null for anonymous renderers.
     ContainerNode* node() const { return toContainerNode(RenderObject::node()); }
 
+    bool hasCompositedLayerMapping() const;
     CompositedLayerMapping* compositedLayerMapping() const;
 
 protected:
     void createLayer();
 
     virtual void willBeDestroyed() OVERRIDE;
 
     virtual void addLayerHitTestRects(LayerHitTestRects&, const RenderLayer*, const LayoutPoint&, const LayoutRect&) const OVERRIDE;
 
 private:
     virtual bool isLayerModelObject() const OVERRIDE FINAL { return true; }
 
     RenderLayer* m_layer;
 
     // Used to store state between styleWillChange and styleDidChange
     static bool s_wasFloating;
     static bool s_hadLayer;
     static bool s_hadTransform;
     static bool s_layerWasSelfPainting;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderLayerModelObject, isLayerModelObject());
 
 } // namespace WebCore
 
 #endif // RenderLayerModelObject_h