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

Source/core/page/Page.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All Rights Reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 612 matching lines @@
 
     return relevantViewRect;
 }
 
 void Page::addRelevantRepaintedObject(RenderObject* object, const LayoutRect& objectPaintRect)
 {
     if (!isCountingRelevantRepaintedObjects())
         return;
 
     // Objects inside sub-frames are not considered to be relevant.
-    if (object->document()->frame() != mainFrame())
+    if (object->document().frame() != mainFrame())
         return;
 
     RenderView* view = object->view();
     if (!view)
         return;
 
     LayoutRect relevantRect = relevantViewRect(view);
 
     // The objects are only relevant if they are being painted within the viewRect().
     if (!objectPaintRect.intersects(pixelSnappedIntRect(relevantRect)))
@@ skipping 104 matching lines @@
     , dragClient(0)
     , inspectorClient(0)
 {
 }
 
 Page::PageClients::~PageClients()
 {
 }
 
 } // namespace WebCore