Add toHTMLDocument() convenience methods that take a reference

Source/core/html/HTMLDocument.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009 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 94 matching lines @@
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isHTMLDocument());
     return static_cast<HTMLDocument*>(document);
 }
 
 inline const HTMLDocument* toHTMLDocument(const Document* document)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isHTMLDocument());
     return static_cast<const HTMLDocument*>(document);
 }
 
+inline HTMLDocument& toHTMLDocument(Document& document)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(document.isHTMLDocument());
+    return static_cast<HTMLDocument&>(document);
+}
+
+inline const HTMLDocument& toHTMLDocument(const Document& document)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(document.isHTMLDocument());
+    return static_cast<const HTMLDocument&>(document);
+}
+
 // This will catch anyone doing an unnecessary cast.
 void toHTMLDocument(const HTMLDocument*);
 
 } // namespace WebCore
 
 #endif // HTMLDocument_h