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

Source/core/rendering/RenderListMarker.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Andrew Wellington (proton@wiretapped.net)
  * Copyright (C) 2010 Daniel Bates (dbates@intudata.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
@@ skipping 1052 matching lines @@
 }
 
 RenderListMarker::~RenderListMarker()
 {
     if (m_image)
         m_image->removeClient(this);
 }
 
 RenderListMarker* RenderListMarker::createAnonymous(RenderListItem* item)
 {
-    Document* document = item->document();
+    Document& document = item->document();
     RenderListMarker* renderer = new RenderListMarker(item);
-    renderer->setDocumentForAnonymous(document);
+    renderer->setDocumentForAnonymous(&document);
     return renderer;
 }
 
 void RenderListMarker::styleWillChange(StyleDifference diff, const RenderStyle* newStyle)
 {
     if (style() && (newStyle->listStylePosition() != style()->listStylePosition() || newStyle->listStyleType() != style()->listStyleType()))
         setNeedsLayoutAndPrefWidthsRecalc();
 
     RenderBox::styleWillChange(diff, newStyle);
 }
@@ skipping 754 matching lines @@
 
     if (clipToVisibleContent)
         computeRectForRepaint(repaintContainer, rect);
     else
         rect = localToContainerQuad(FloatRect(rect), repaintContainer).enclosingBoundingBox();
 
     return rect;
 }
 
 } // namespace WebCore