Implemented XMLSerializer in PrivateScript.

Source/core/xml/XMLSerializer.h

 /*
  *  Copyright (C) 2003, 2006 Apple Computer, Inc.
  *  Copyright (C) 2006 Samuel Weinig (sam@webkit.org)
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser 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 21 matching lines @@
 class Node;
 
 class XMLSerializer FINAL : public RefCountedWillBeGarbageCollected<XMLSerializer>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PassRefPtrWillBeRawPtr<XMLSerializer> create()
     {
         return adoptRefWillBeNoop(new XMLSerializer);
     }
 
-    String serializeToString(Node*, ExceptionState&);
-
     void trace(Visitor*) { }
 
 private:
     XMLSerializer()
     {
         ScriptWrappable::init(this);
     }
 };
 
 } // namespace blink
 
 #endif // XMLSerializer_h