Make ensureCompositedMappingLayer() to be a void function.

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 265 matching lines @@
     void operator delete(void*);
 
     CompositingState compositingState() const;
 
     // This returns true if our document is in a phase of its lifestyle during which
     // compositing state may legally be read.
     bool isAllowedToQueryCompositingState() const;
 
     // Don't null check this.
     CompositedLayerMapping* compositedLayerMapping() const;
-    // FIXME: This should return a reference.
-    CompositedLayerMapping* ensureCompositedLayerMapping();
     GraphicsLayer* graphicsLayerBacking() const;
     GraphicsLayer* graphicsLayerBackingForScrolling() const;
     // NOTE: If you are using hasCompositedLayerMapping to determine the state of compositing for this layer,
     // (and not just to do bookkeeping related to the mapping like, say, allocating or deallocating a mapping),
     // then you may have incorrect logic. Use compositingState() instead.
     // FIXME: This is identical to null checking compositedLayerMapping(), why not just call that?
     bool hasCompositedLayerMapping() const { return m_compositedLayerMapping.get(); }
+    void ensureCompositedLayerMapping();
     void clearCompositedLayerMapping(bool layerBeingDestroyed = false);
     CompositedLayerMapping* groupedMapping() const { return m_groupedMapping; }
     void setGroupedMapping(CompositedLayerMapping* groupedMapping, bool layerBeingDestroyed = false);
 
     bool hasCompositedMask() const;
     bool hasCompositedClippingMask() const;
     bool needsCompositedScrolling() const { return m_scrollableArea && m_scrollableArea->needsCompositedScrolling(); }
 
     // Computes the position of the given render object in the space of |paintInvalidationContainer|.
     // FIXME: invert the logic to have paint invalidation containers take care of painting objects into them, rather than the reverse.
@@ skipping 377 matching lines @@
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const blink::RenderLayer*);
 void showLayerTree(const blink::RenderObject*);
 #endif
 
 #endif // RenderLayer_h