ppapi: Cleanup class/struct forward declarations

ppapi/proxy/video_decoder_resource.h

 // Copyright (c) 2014 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_PROXY_VIDEO_DECODER_RESOURCE_H_
 #define PPAPI_PROXY_VIDEO_DECODER_RESOURCE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 12 matching lines @@
 
 namespace gpu {
 struct Mailbox;
 namespace gles2 {
 class GLES2Implementation;
 }
 }
 
 namespace ppapi {
 
-class PPB_Graphics3D_Shared;
 class TrackedCallback;
 
 namespace proxy {
 
 class PPAPI_PROXY_EXPORT VideoDecoderResource
     : public PluginResource,
       public thunk::PPB_VideoDecoder_API {
  public:
   VideoDecoderResource(Connection connection, PP_Instance instance);
   ~VideoDecoderResource() override;
@@ skipping 146 matching lines @@
   bool testing_;
   int32_t decoder_last_error_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoDecoderResource);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_VIDEO_DECODER_RESOURCE_H_