Have DOMImplementation take the Document argument by reference

Source/core/dom/DOMImplementation.h

Index: Source/core/dom/DOMImplementation.h
diff --git a/Source/core/dom/DOMImplementation.h b/Source/core/dom/DOMImplementation.h
index 5fb1f514bf33a6e27f173395ca67469fbbda612e..76852d3ef05c00bd27116705c0e4542a59f95fd9 100644
--- a/Source/core/dom/DOMImplementation.h
+++ b/Source/core/dom/DOMImplementation.h
@@ -42,11 +42,11 @@ 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);
@@ -69,9 +69,9 @@ public:
     static bool isTextMIMEType(const String& MIMEType);
 
 private:
-    explicit DOMImplementation(Document*);
+    explicit DOMImplementation(Document&);
 
-    Document* m_document;
+    Document& m_document;
 };
 
 } // namespace WebCore