Clean up forward declarations in Source/platform

Source/platform/graphics/ImageDecodingStore.h

 /*
  * Copyright (C) 2012 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:
  * 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 24 matching lines @@
 #include "wtf/DoublyLinkedList.h"
 #include "wtf/HashSet.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/ThreadingPrimitives.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class ImageFrameGenerator;
-class SharedBuffer;
 
 // FUNCTION
 //
 // ImageDecodingStore is a class used to manage cached decoder objects.
 //
 // EXTERNAL OBJECTS
 //
 // ImageDecoder
 //   A decoder object. It is used to decode raw data into bitmap images.
 //
@@ skipping 156 matching lines @@
     //   m_heapLimitInBytes
     //   m_heapMemoryUsageInBytes
     // This mutex also protects calls to underlying skBitmap's
     // lockPixels()/unlockPixels() as they are not threadsafe.
     Mutex m_mutex;
 };
 
 } // namespace blink
 
 #endif