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

Source/core/inspector/DOMPatchSupport.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 484 matching lines @@
         Digest* first = queue.takeFirst();
         m_unusedNodesMap.remove(first->m_sha1);
         for (size_t i = 0; i < first->m_children.size(); ++i)
             queue.append(first->m_children[i].get());
     }
 }
 
 #ifdef DEBUG_DOM_PATCH_SUPPORT
 static String nodeName(Node* node)
 {
-    if (node->document()->isXHTMLDocument())
+    if (node->document().isXHTMLDocument())
          return node->nodeName();
     return node->nodeName().lower();
 }
 
 void DOMPatchSupport::dumpMap(const ResultMap& map, const String& name)
 {
     fprintf(stderr, "\n\n");
     for (size_t i = 0; i < map.size(); ++i)
         fprintf(stderr, "%s[%lu]: %s (%p) - [%lu]\n", name.utf8().data(), i, map[i].first ? nodeName(map[i].first->m_node).utf8().data() : "", map[i].first, map[i].second);
 }
 #endif
 
 } // namespace WebCore