Have DOMImplementation::document() return reference.

Source/core/css/StyleSheetList.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 25 matching lines @@
 class StyleSheetList : public RefCounted<StyleSheetList> {
 public:
     static PassRefPtr<StyleSheetList> create(TreeScope* treeScope) { return adoptRef(new StyleSheetList(treeScope)); }
     ~StyleSheetList();
 
     unsigned length();
     StyleSheet* item(unsigned index);
 
     HTMLStyleElement* getNamedItem(const AtomicString&) const;
 
-    // FIXME: Should return a reference.
-    Document* document() { return &m_treeScope->document(); }
+    Document& document() { return m_treeScope->document(); }
 
     void detachFromDocument();
     CSSStyleSheet* anonymousNamedGetter(const AtomicString&);
 
 private:
     StyleSheetList(TreeScope*);
     const Vector<RefPtr<StyleSheet> >& styleSheets();
 
     TreeScope* m_treeScope;
     Vector<RefPtr<StyleSheet> > m_detachedStyleSheets;
 };
 
 } // namespace WebCore
 
 #endif // StyleSheetList_h