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

Source/core/html/HTMLAreaElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2009, 2011 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 124 matching lines @@
     if (shape == Unknown) {
         if (m_coords.size() == 3)
             shape = Circle;
         else if (m_coords.size() == 4)
             shape = Rect;
         else if (m_coords.size() >= 6)
             shape = Poly;
     }
 
     Path path;
-    RenderView* renderView = document()->renderView();
+    RenderView* renderView = document().renderView();
     switch (shape) {
         case Poly:
             if (m_coords.size() >= 6) {
                 int numPoints = m_coords.size() / 2;
                 path.moveTo(FloatPoint(minimumValueForLength(m_coords[0], width, renderView), minimumValueForLength(m_coords[1], height, renderView)));
                 for (int i = 1; i < numPoints; ++i)
                     path.addLineTo(FloatPoint(minimumValueForLength(m_coords[i * 2], width, renderView), minimumValueForLength(m_coords[i * 2 + 1], height, renderView)));
                 path.closeSubpath();
             }
             break;
@@ skipping 90 matching lines @@
     // FIXME: This means that an AREA that is not a link cannot be made focusable through contenteditable or tabindex. Is it correct?
     return isLink();
 }
 
 String HTMLAreaElement::target() const
 {
     return getAttribute(targetAttr);
 }
 
 }