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

Source/core/css/resolver/MatchedPropertiesCache.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 97 matching lines @@
     }
     for (size_t i = 0; i < toRemove.size(); ++i)
         m_cache.remove(toRemove[i]);
 
     m_additionsSinceLastSweep = 0;
 }
 
 bool MatchedPropertiesCache::isCacheable(const Element* element, const RenderStyle* style, const RenderStyle* parentStyle)
 {
     // FIXME: CSSPropertyWebkitWritingMode modifies state when applying to document element. We can't skip the applying by caching.
-    if (element == element->document()->documentElement() && element->document()->writingModeSetOnDocumentElement())
+    if (element == element->document().documentElement() && element->document().writingModeSetOnDocumentElement())
         return false;
     if (style->unique() || (style->styleType() != NOPSEUDO && parentStyle->unique()))
         return false;
     if (style->hasAppearance())
         return false;
     if (style->zoom() != RenderStyle::initialZoom())
         return false;
     if (style->writingMode() != RenderStyle::initialWritingMode())
         return false;
     // The cache assumes static knowledge about which properties are inherited.
     if (parentStyle->hasExplicitlyInheritedProperties())
         return false;
     return true;
 }
 
 }