Prefer to forward-declare GraphicsContext in headers.

Source/core/rendering/svg/RenderSVGResourceMasker.h

 /*
  * Copyright (C) Research In Motion Limited 2009-2010. 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.
  *
  * 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 RenderSVGResourceMasker_h
 #define RenderSVGResourceMasker_h
 
 #include "core/rendering/svg/RenderSVGResourceContainer.h"
 #include "core/svg/SVGMaskElement.h"
 #include "core/svg/SVGUnitTypes.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/IntSize.h"
-#include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/ImageBuffer.h"
 
 #include "wtf/HashMap.h"
 #include "wtf/OwnPtr.h"
 
 namespace WebCore {
 
 class DisplayList;
+class GraphicsContext;
 
 class RenderSVGResourceMasker FINAL : public RenderSVGResourceContainer {
 public:
     explicit RenderSVGResourceMasker(SVGMaskElement*);
     virtual ~RenderSVGResourceMasker();
 
     virtual const char* renderName() const OVERRIDE { return "RenderSVGResourceMasker"; }
 
     virtual void removeAllClientsFromCache(bool markForInvalidation = true) OVERRIDE;
     virtual void removeClientFromCache(RenderObject*, bool markForInvalidation = true) OVERRIDE;
@@ skipping 14 matching lines @@
 
     RefPtr<DisplayList> m_maskContentDisplayList;
     FloatRect m_maskContentBoundaries;
 };
 
 DEFINE_RENDER_SVG_RESOURCE_TYPE_CASTS(RenderSVGResourceMasker, MaskerResourceType);
 
 }
 
 #endif