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

Source/core/css/resolver/ScopedStyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 125 matching lines @@
             if (ScopedStyleResolver* resolver = scopedStyleResolverFor(shadowRoot))
                 resolvers.append(resolver);
         }
         if (!shadowRoot->containsShadowElements())
             break;
     }
 }
 
 void ScopedStyleTree::resolveScopedKeyframesRules(const Element* element, Vector<ScopedStyleResolver*, 8>& resolvers)
 {
-    Document* document = element->document();
+    Document& document = element->document();
     TreeScope* treeScope = element->treeScope();
     bool applyAuthorStyles = treeScope->applyAuthorStyles();
 
     for (ScopedStyleResolver* scopedResolver = scopedResolverFor(element); scopedResolver; scopedResolver = scopedResolver->parent()) {
-        if (scopedResolver->treeScope() == treeScope || (applyAuthorStyles && scopedResolver->treeScope() == document))
+        if (scopedResolver->treeScope() == treeScope || (applyAuthorStyles && scopedResolver->treeScope() == &document))
             resolvers.append(scopedResolver);
     }
 }
 
 inline ScopedStyleResolver* ScopedStyleTree::enclosingScopedStyleResolverFor(const ContainerNode* scopingNode)
 {
     for (; scopingNode; scopingNode = scopingNode->parentOrShadowHostNode()) {
         if (ScopedStyleResolver* scopedStyleResolver = scopedStyleResolverFor(scopingNode))
             return scopedStyleResolver;
     }
@@ skipping 265 matching lines @@
     collector.matchPageRules(m_authorStyle.get());
 }
 
 void ScopedStyleResolver::collectViewportRulesTo(StyleResolver* resolver) const
 {
     if (m_authorStyle)
         resolver->collectViewportRules(m_authorStyle.get());
 }
 
 } // namespace WebCore