content: Cleanup class/struct forward declarations

content/renderer/media/media_stream_source.h

 // Copyright 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 CONTENT_RENDERER_MEDIA_MEDIA_STREAM_SOURCE_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_SOURCE_H_
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "content/common/content_export.h"
 #include "content/common/media/media_stream_options.h"
 #include "third_party/WebKit/public/platform/WebMediaStreamSource.h"
 
-namespace blink {
-class WebMediaStreamTrack;
-}  // namespace blink
-
 namespace content {
 
 class CONTENT_EXPORT MediaStreamSource
     : NON_EXPORTED_BASE(public blink::WebMediaStreamSource::ExtraData) {
  public:
   typedef base::Callback<void(const blink::WebMediaStreamSource& source)>
       SourceStoppedCallback;
 
   typedef base::Callback<void(MediaStreamSource* source,
                               MediaStreamRequestResult result,
@@ skipping 41 matching lines @@
   // In debug builds, check that all methods are being called on the main
   // thread.
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaStreamSource);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_SOURCE_H_