Prefer to forward-declare GraphicsContext in headers.

Source/platform/graphics/ImageBuffer.h

 /*
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 15 matching lines @@
  */
 
 #ifndef ImageBuffer_h
 #define ImageBuffer_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/IntSize.h"
 #include "platform/graphics/Canvas2DLayerBridge.h"
 #include "platform/graphics/ColorSpace.h"
-#include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/GraphicsTypes3D.h"
 #include "platform/graphics/ImageBufferSurface.h"
 #include "platform/transforms/AffineTransform.h"
 #include "wtf/Forward.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/Uint8ClampedArray.h"
 #include "wtf/Vector.h"
 
 class SkCanvas;
 
 namespace blink {
 class WebGraphicsContext3D;
 }
 
 namespace WebCore {
 
 class DrawingBuffer;
+class GraphicsContext;
 class Image;
 class ImageBufferClient;
 class IntPoint;
 class IntRect;
 
 enum Multiply {
     Premultiplied,
     Unmultiplied
 };
 
@@ skipping 82 matching lines @@
 
     IntSize m_size;
     RefPtr<Uint8ClampedArray> m_data;
 };
 
 String PLATFORM_EXPORT ImageDataToDataURL(const ImageDataBuffer&, const String& mimeType, const double* quality);
 
 } // namespace WebCore
 
 #endif // ImageBuffer_h