Make ensureCompositedMappingLayer() to be a void function.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. 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>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 2405 matching lines @@
     switch (compositingState()) {
     case NotComposited:
         return 0;
     case PaintsIntoGroupedBacking:
         return groupedMapping()->squashingLayer();
     default:
         return compositedLayerMapping()->scrollingContentsLayer() ? compositedLayerMapping()->scrollingContentsLayer() : compositedLayerMapping()->mainGraphicsLayer();
     }
 }
 
-CompositedLayerMapping* RenderLayer::ensureCompositedLayerMapping()
+void RenderLayer::ensureCompositedLayerMapping()
 {
-    if (!m_compositedLayerMapping) {
-        m_compositedLayerMapping = adoptPtr(new CompositedLayerMapping(*this));
-        m_compositedLayerMapping->setNeedsGraphicsLayerUpdate(GraphicsLayerUpdateSubtree);
+    if (m_compositedLayerMapping)
+        return;
 
-        updateOrRemoveFilterEffectRenderer();
-    }
-    return m_compositedLayerMapping.get();
+    m_compositedLayerMapping = adoptPtr(new CompositedLayerMapping(*this));
+    m_compositedLayerMapping->setNeedsGraphicsLayerUpdate(GraphicsLayerUpdateSubtree);
+
+    updateOrRemoveFilterEffectRenderer();
 }
 
 void RenderLayer::clearCompositedLayerMapping(bool layerBeingDestroyed)
 {
     if (!layerBeingDestroyed) {
         // We need to make sure our decendants get a geometry update. In principle,
         // we could call setNeedsGraphicsLayerUpdate on our children, but that would
         // require walking the z-order lists to find them. Instead, we over-invalidate
         // by marking our parent as needing a geometry update.
         if (RenderLayer* compositingParent = enclosingLayerWithCompositedLayerMapping(ExcludeSelf))
@@ skipping 394 matching lines @@
     }
 }
 
 void showLayerTree(const blink::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif