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

Source/core/rendering/svg/RenderSVGResourceContainer.cpp

 /*
  * Copyright (C) Research In Motion Limited 2010. 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 15 matching lines @@
 #include "core/rendering/svg/RenderSVGRoot.h"
 #include "core/rendering/svg/SVGRenderingContext.h"
 #include "core/rendering/svg/SVGResourcesCache.h"
 #include "core/svg/SVGGraphicsElement.h"
 
 namespace WebCore {
 
 static inline SVGDocumentExtensions* svgExtensionsFromNode(Node* node)
 {
     ASSERT(node);
-    ASSERT(node->document());
-    return node->document()->accessSVGExtensions();
+    return node->document().accessSVGExtensions();
 }
 
 RenderSVGResourceContainer::RenderSVGResourceContainer(SVGElement* node)
     : RenderSVGHiddenContainer(node)
     , m_id(node->getIdAttribute())
     , m_registered(false)
     , m_isInvalidating(false)
 {
 }
 
@@ skipping 169 matching lines @@
     if (!object->isSVGShape())
         return resourceTransform;
 
     SVGGraphicsElement* element = toSVGGraphicsElement(object->node());
     AffineTransform transform = element->getScreenCTM(SVGLocatable::DisallowStyleUpdate);
     transform *= resourceTransform;
     return transform;
 }
 
 }