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

Source/core/svg/SVGImageLoader.cpp

 /*
  * Copyright (C) 2005, 2005 Alexander Kellett <lypanov@kde.org>
  * Copyright (C) 2008 Rob Buis <buis@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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 33 matching lines @@
         if (imageElement->externalResourcesRequiredBaseValue())
             imageElement->sendSVGLoadEventIfPossible(true);
     }
 }
 
 String SVGImageLoader::sourceURI(const AtomicString& attribute) const
 {
     KURL base = element()->baseURI();
     if (base.isValid())
         return KURL(base, stripLeadingAndTrailingHTMLSpaces(attribute)).string();
-    return element()->document()->completeURL(stripLeadingAndTrailingHTMLSpaces(attribute));
+    return element()->document().completeURL(stripLeadingAndTrailingHTMLSpaces(attribute));
 }
 
 }