Cleanup: Remove unneeded forward declarations in ppapi.

ppapi/cpp/image_data.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_CPP_IMAGE_DATA_H_
 #define PPAPI_CPP_IMAGE_DATA_H_
 
 #include "ppapi/c/ppb_image_data.h"
 #include "ppapi/cpp/point.h"
 #include "ppapi/cpp/size.h"
 #include "ppapi/cpp/resource.h"
 
 
 /// @file
 /// This file defines the APIs for determining how a browser
 /// handles image data.
 namespace pp {
 
 class Instance;
-class Plugin;
 
 class ImageData : public Resource {
  public:
   /// Default constructor for creating an is_null() <code>ImageData</code>
   /// object.
   ImageData();
 
   /// A special structure used by the constructor that does not increment the
   /// reference count of the underlying Image resource.
   struct PassRef {};
@@ skipping 95 matching lines @@
  private:
   void PassRefAndInitData(PP_Resource resource);
 
   PP_ImageDataDesc desc_;
   void* data_;
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_IMAGE_DATA_H_