Reduce number of header includes in SVG

Source/core/svg/SVGElementInstanceList.h

 /*
  * Copyright (C) 2007 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef SVGElementInstanceList_h
 #define SVGElementInstanceList_h
 
 #include "bindings/v8/ScriptWrappable.h"
-#include "core/svg/SVGElementInstance.h"
 #include "wtf/RefCounted.h"
 
 namespace WebCore {
 
+class SVGElementInstance;
+
 class SVGElementInstanceList : public RefCounted<SVGElementInstanceList>, public ScriptWrappable {
 public:
     static PassRefPtr<SVGElementInstanceList> create(PassRefPtr<SVGElementInstance> root) { return adoptRef(new SVGElementInstanceList(root)); }
     virtual ~SVGElementInstanceList();
 
     unsigned length() const;
     SVGElementInstance* item(unsigned index);
 
 private:
     SVGElementInstanceList(PassRefPtr<SVGElementInstance>);
 
     RefPtr<SVGElementInstance> m_rootInstance;
 };
 
 } // namespace WebCore
 
 #endif