Prefer to forward-declare GraphicsContext in headers.

Source/core/html/canvas/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple Inc. 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 59 matching lines @@
 #include "core/html/canvas/WebGLShaderPrecisionFormat.h"
 #include "core/html/canvas/WebGLTexture.h"
 #include "core/html/canvas/WebGLUniformLocation.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/loader/FrameLoader.h"
 #include "core/loader/FrameLoaderClient.h"
 #include "core/rendering/RenderBox.h"
 #include "platform/CheckedInt.h"
 #include "platform/NotImplemented.h"
 #include "platform/geometry/IntSize.h"
+#include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/UnacceleratedImageBufferSurface.h"
 #include "platform/graphics/gpu/DrawingBuffer.h"
 #include "public/platform/Platform.h"
 
 #include "wtf/PassOwnPtr.h"
 #include "wtf/Uint32Array.h"
 #include "wtf/text/StringBuilder.h"
 
 namespace WebCore {
 
@@ skipping 5595 matching lines @@
         if (m_textureUnits[i].m_texture2DBinding
             || m_textureUnits[i].m_textureCubeMapBinding) {
             m_onePlusMaxNonDefaultTextureUnit = i + 1;
             return;
         }
     }
     m_onePlusMaxNonDefaultTextureUnit = 0;
 }
 
 } // namespace WebCore