Remove obsolete forward declarations from SVGDocument.

Source/core/svg/SVGDocument.h

 /*
  * Copyright (C) 2004, 2005 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@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 SVGDocument_h
 #define SVGDocument_h
 
 #include "core/dom/Document.h"
 #include "core/platform/graphics/FloatPoint.h"
 
 namespace WebCore {
 
-class DOMImplementation;
-class SVGElement;
 class SVGSVGElement;
 
 class SVGDocument FINAL : public Document {
 public:
     static PassRefPtr<SVGDocument> create(const DocumentInit& initializer = DocumentInit())
     {
         return adoptRef(new SVGDocument(initializer));
     }
 
     SVGSVGElement* rootElement() const;
 
     void dispatchZoomEvent(float prevScale, float newScale);
     void dispatchScrollEvent();
 
     bool zoomAndPanEnabled() const;
 
     void startPan(const FloatPoint& start);
     void updatePan(const FloatPoint& pos) const;
 
 private:
-    SVGDocument(const DocumentInit&);
+    explicit SVGDocument(const DocumentInit&);
 
     virtual bool childShouldCreateRenderer(const NodeRenderingContext&) const;
 
     FloatPoint m_translate;
 };
 
 inline SVGDocument* toSVGDocument(Document* document)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isSVGDocument());
     return static_cast<SVGDocument*>(document);
 }
 
 inline const SVGDocument* toSVGDocument(const Document* document)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isSVGDocument());
     return static_cast<const SVGDocument*>(document);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toSVGDocument(const SVGDocument*);
 
 } // namespace WebCore
 
 #endif // SVGDocument_h