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

Source/core/dom/Position.h

 /*
  * Copyright (C) 2004, 2006, 2008 Apple 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 109 matching lines @@
     Node* computeNodeBeforePosition() const;
     Node* computeNodeAfterPosition() const;
 
     Node* anchorNode() const { return m_anchorNode.get(); }
 
     // FIXME: Callers should be moved off of node(), node() is not always the container for this position.
     // For nodes which editingIgnoresContent(node()) returns true, positions like [ignoredNode, 0]
     // will be treated as before ignoredNode (thus node() is really after the position, not containing it).
     Node* deprecatedNode() const { return m_anchorNode.get(); }
 
-    Document* document() const { return m_anchorNode ? m_anchorNode->document() : 0; }
+    Document* document() const { return m_anchorNode ? &m_anchorNode->document() : 0; }
     Element* rootEditableElement() const
     {
         Node* container = containerNode();
         return container ? container->rootEditableElement() : 0;
     }
 
     // These should only be used for PositionIsOffsetInAnchor positions, unless
     // the position is a legacy editing position.
     void moveToPosition(PassRefPtr<Node> anchorNode, int offset);
     void moveToOffset(int offset);
@@ skipping 198 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const WebCore::Position&);
 void showTree(const WebCore::Position*);
 #endif
 
 #endif // Position_h