Sync the DOMImplementation interface with the spec

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 42 matching lines @@
 #endif
     Document& document() const { return *m_document; }
 
     // DOM methods & attributes for DOMImplementation
     static bool hasFeature(const String& feature, const String& version);
     bool hasFeatureForBindings(const String& feature, const String& version);
     PassRefPtrWillBeRawPtr<DocumentType> createDocumentType(const AtomicString& qualifiedName, const String& publicId, const String& systemId, ExceptionState&);
     PassRefPtrWillBeRawPtr<XMLDocument> createDocument(const AtomicString& namespaceURI, const AtomicString& qualifiedName, DocumentType*, ExceptionState&);
 
     // From the HTMLDOMImplementation interface
-    PassRefPtrWillBeRawPtr<HTMLDocument> createHTMLDocument(const String& title);
+    PassRefPtrWillBeRawPtr<HTMLDocument> createHTMLDocument(const String& title = String());
 
     // Other methods (not part of DOM)
     static PassRefPtrWillBeRawPtr<Document> createDocument(const String& mimeType, const DocumentInit&, bool inViewSourceMode);
 
     static bool isXMLMIMEType(const String&);
     static bool isTextMIMEType(const String&);
     static bool isJSONMIMEType(const String&);
 
     DECLARE_TRACE();
 
 private:
     explicit DOMImplementation(Document&);
 
     RawPtrWillBeMember<Document> m_document;
 };
 
 } // namespace blink
 
 #endif // DOMImplementation_h