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

Source/core/dom/Node.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.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 466 matching lines @@
     // This does not 100% guarantee the user can see it, but is pretty close.
     // Note: This method only works properly after layout has occurred.
     bool hasNonEmptyBoundingBox() const;
 
     unsigned nodeIndex() const;
 
     // Returns the DOM ownerDocument attribute. This method never returns NULL, except in the case
     // of a Document node.
     Document* ownerDocument() const;
 
-    // FIXME: This should return a reference.
-    // Returns the document associated with this node. This method never returns 0.
-    // A Document node returns itself.
-    Document* document() const
+    // Returns the document associated with this node. A Document node returns itself.
+    Document& document() const
     {
         ASSERT(this);
         ASSERT(documentInternal());
-        return documentInternal();
+        return *documentInternal();
     }
 
     TreeScope* treeScope() const { return m_treeScope; }
 
     // Returns true if this node is associated with a document and is in its associated document's
     // node tree, false otherwise.
     bool inDocument() const
     {
         ASSERT(documentInternal() || !getFlag(InDocumentFlag));
         return getFlag(InDocumentFlag);
@@ skipping 438 matching lines @@
 
 } //namespace
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const WebCore::Node*);
 void showNodePath(const WebCore::Node*);
 #endif
 
 #endif