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

Source/core/svg/SVGImageElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Rob Buis <buis@kde.org>
  * Copyright (C) 2006 Alexander Kellett <lypanov@kde.org>
  *
  * 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.
  *
@@ skipping 205 matching lines @@
 
 const AtomicString& SVGImageElement::imageSourceURL() const
 {
     return getAttribute(XLinkNames::hrefAttr);
 }
 
 void SVGImageElement::addSubresourceAttributeURLs(ListHashSet<KURL>& urls) const
 {
     SVGGraphicsElement::addSubresourceAttributeURLs(urls);
 
-    addSubresourceURL(urls, document()->completeURL(hrefCurrentValue()));
+    addSubresourceURL(urls, document().completeURL(hrefCurrentValue()));
 }
 
 void SVGImageElement::didMoveToNewDocument(Document* oldDocument)
 {
     m_imageLoader.elementDidMoveToNewDocument();
     SVGGraphicsElement::didMoveToNewDocument(oldDocument);
 }
 
 }