Have DOMImplementation take the Document argument by reference

Source/core/dom/DOMImplementation.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, 2008 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.
@@ skipping 24 matching lines @@
 class DocumentInit;
 class DocumentType;
 class ExceptionState;
 class Frame;
 class HTMLDocument;
 class KURL;
 
 class DOMImplementation : public ScriptWrappable {
     WTF_MAKE_FAST_ALLOCATED;
 public:
-    static PassOwnPtr<DOMImplementation> create(Document* document) { return adoptPtr(new DOMImplementation(document)); }
+    static PassOwnPtr<DOMImplementation> create(Document& document) { return adoptPtr(new DOMImplementation(document)); }
 
-    void ref() { m_document->ref(); }
-    void deref() { m_document->deref(); }
-    Document* document() { return m_document; }
+    void ref() { m_document.ref(); }
+    void deref() { m_document.deref(); }
+    Document* document() { return &m_document; }
 
     // DOM methods & attributes for DOMImplementation
     static bool hasFeature(const String& feature, const String& version);
     PassRefPtr<DocumentType> createDocumentType(const String& qualifiedName, const String& publicId, const String& systemId, ExceptionState&);
     PassRefPtr<Document> createDocument(const String& namespaceURI, const String& qualifiedName, DocumentType*, ExceptionState&);
 
     DOMImplementation* getInterface(const String& feature);
 
     // From the DOMImplementationCSS interface
     static PassRefPtr<CSSStyleSheet> createCSSStyleSheet(const String& title, const String& media);
 
     // From the HTMLDOMImplementation interface
     PassRefPtr<HTMLDocument> createHTMLDocument(const String& title);
 
     // Other methods (not part of DOM)
     static PassRefPtr<Document> createDocument(const String& MIMEType, Frame*, const KURL&, bool inViewSourceMode);
     static PassRefPtr<Document> createDocument(const String& type, const DocumentInit&, bool inViewSourceMode);
 
     static bool isXMLMIMEType(const String& MIMEType);
     static bool isTextMIMEType(const String& MIMEType);
 
 private:
-    explicit DOMImplementation(Document*);
+    explicit DOMImplementation(Document&);
 
-    Document* m_document;
+    Document& m_document;
 };
 
 } // namespace WebCore
 
 #endif