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

Source/core/dom/ContainerNodeAlgorithms.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, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 72 matching lines @@
         // If we have been added to the document during this loop, then we
         // don't want to tell the rest of our children that they've been
         // removed from the document because they haven't.
         if (!node->inDocument() && child->parentNode() == node)
             notifyNodeRemovedFromDocument(child.get());
     }
 
     if (!node->isElementNode())
         return;
 
-    if (node->document()->cssTarget() == node)
-        node->document()->setCSSTarget(0);
+    if (node->document().cssTarget() == node)
+        node->document().setCSSTarget(0);
 
     if (ElementShadow* shadow = toElement(node)->shadow()) {
         ShadowRootVector roots(shadow);
         for (size_t i = 0; i < roots.size(); ++i) {
             if (!node->inDocument() && roots[i]->host() == node)
                 notifyNodeRemovedFromDocument(roots[i].get());
         }
     }
 }
 
@@ skipping 45 matching lines @@
     // If we overcount it's safe, but not optimal because it means we'll traverse
     // through the document in ChildFrameDisconnector looking for frames that have
     // already been disconnected.
     ASSERT(node->connectedSubframeCount() == count);
 
     return count;
 }
 #endif
 
 }