Clean up forward declarations in Source/platform

Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * Copyright (c) 2010, Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 32 matching lines @@
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "wtf/Deque.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
 class Extensions3DUtil;
 class ImageBuffer;
-class ImageData;
 class WebExternalBitmap;
 class WebExternalTextureLayer;
 class WebGraphicsContext3D;
 class WebLayer;
 
 // Abstract interface to allow basic context eviction management
 class PLATFORM_EXPORT ContextEvictionManager : public RefCounted<ContextEvictionManager> {
 public:
     virtual ~ContextEvictionManager() {};
 
@@ skipping 233 matching lines @@
     // used to resize the Canvas.
     SkBitmap m_resizingBitmap;
 
     // Used to flip a bitmap vertically.
     Vector<uint8_t> m_scanline;
 };
 
 } // namespace blink
 
 #endif // DrawingBuffer_h