Have Node::document() return a reference instead of a pointer

Source/core/rendering/RenderLayerFilterInfo.cpp

 /*
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 108 matching lines @@
         DocumentResourceReference* documentReference = referenceFilterOperation->documentResourceReference();
         DocumentResource* cachedSVGDocument = documentReference ? documentReference->document() : 0;
 
         if (cachedSVGDocument) {
             // Reference is external; wait for notifyFinished().
             cachedSVGDocument->addClient(this);
             m_externalSVGReferences.append(cachedSVGDocument);
         } else {
             // Reference is internal; add layer as a client so we can trigger
             // filter repaint on SVG attribute change.
-            Element* filter = m_layer->renderer()->node()->document()->getElementById(referenceFilterOperation->fragment());
+            Element* filter = m_layer->renderer()->node()->document().getElementById(referenceFilterOperation->fragment());
             if (!filter || !filter->hasTagName(SVGNames::filterTag))
                 continue;
             toSVGFilterElement(filter)->addClientRenderLayer(m_layer);
             m_internalSVGReferences.append(filter);
         }
     }
 }
 
 void RenderLayerFilterInfo::removeReferenceFilterClients()
 {
@@ skipping 37 matching lines @@
 
 void RenderLayerFilterInfo::removeCustomFilterClients()
 {
     for (size_t i = 0; i < m_cachedCustomFilterPrograms.size(); ++i)
         m_cachedCustomFilterPrograms.at(i)->removeClient(this);
     m_cachedCustomFilterPrograms.clear();
 }
 
 } // namespace WebCore