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

Source/core/dom/DocumentFragment.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2009 Apple Inc. 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.
@@ skipping 49 matching lines @@
         case TEXT_NODE:
         case CDATA_SECTION_NODE:
             return true;
         default:
             return false;
     }
 }
 
 PassRefPtr<Node> DocumentFragment::cloneNode(bool deep)
 {
-    RefPtr<DocumentFragment> clone = create(document());
+    RefPtr<DocumentFragment> clone = create(&document());
     if (deep)
         cloneChildNodes(clone.get());
     return clone.release();
 }
 
 void DocumentFragment::parseHTML(const String& source, Element* contextElement, ParserContentPolicy parserContentPolicy)
 {
     HTMLDocumentParser::parseDocumentFragment(source, this, contextElement, parserContentPolicy);
 }
 
 bool DocumentFragment::parseXML(const String& source, Element* contextElement, ParserContentPolicy parserContentPolicy)
 {
     return XMLDocumentParser::parseDocumentFragment(source, this, contextElement, parserContentPolicy);
 }
 
 }