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

Source/core/rendering/RenderListItem.cpp

 /**
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Andrew Wellington (proton@wiretapped.net)
  *
  * 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 203 matching lines @@
 {
     return lastChild() == m_marker;
 }
 
 static RenderObject* getParentOfFirstLineBox(RenderBlock* curr, RenderObject* marker)
 {
     RenderObject* firstChild = curr->firstChild();
     if (!firstChild)
         return 0;
 
-    bool inQuirksMode = curr->document()->inQuirksMode();
+    bool inQuirksMode = curr->document().inQuirksMode();
     for (RenderObject* currChild = firstChild; currChild; currChild = currChild->nextSibling()) {
         if (currChild == marker)
             continue;
 
         if (currChild->isInline() && (!currChild->isRenderInline() || curr->generatesLineBoxesForInlineChild(currChild)))
             return curr;
 
         if (currChild->isFloating() || currChild->isOutOfFlowPositioned())
             continue;
 
@@ skipping 269 matching lines @@
             // assume that all the following ones have too.
             // This gives us the opportunity to stop here and avoid
             // marking the same nodes again.
             break;
         }
         item->updateValue();
     }
 }
 
 } // namespace WebCore