Use a boolean hasCompositedLayerMapping() accessor instead of the pointer

Source/core/rendering/RenderLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 327 matching lines @@
 
     bool hasBlendMode() const;
     bool paintsWithBlendMode() const { return hasBlendMode() && compositingState() != PaintsIntoOwnBacking; }
 
     void* operator new(size_t);
     // Only safe to call from RenderLayerModelObject::destroyLayer()
     void operator delete(void*);
 
     CompositingState compositingState() const;
 
-    // NOTE: If you are accessing the CompositedLayerMapping as a boolean condition to determine the state of compositing for this layer,
-    // then you may have incorrect logic. Use compositingState() instead.
+    bool hasCompositedLayerMapping() const { return m_compositedLayerMapping.get(); }
+    // NOTE: If you are accessing the CompositedLayerMapping() as a boolean condition to determine the state of compositing for this layer,
+    // then you may have incorrect logic. Use compositingState() instead, or if you really know you just care about the existence of
+    // compositedLayerMapping versus the compositing state, use hasCompositedLayerMapping() instead.
     CompositedLayerMapping* compositedLayerMapping() const { return m_compositedLayerMapping.get(); }
     CompositedLayerMapping* ensureCompositedLayerMapping();
     void clearCompositedLayerMapping(bool layerBeingDestroyed = false);
 
     bool hasCompositedMask() const;
     bool hasCompositedClippingMask() const;
     bool needsCompositedScrolling() const { return m_scrollableArea && m_scrollableArea->needsCompositedScrolling(); }
 
     RenderLayer* scrollParent() const;
     RenderLayer* clipParent() const;
@@ skipping 371 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const WebCore::RenderLayer*);
 void showLayerTree(const WebCore::RenderObject*);
 #endif
 
 #endif // RenderLayer_h