content: Cleanup class/struct forward declarations

content/renderer/media/webrtc/media_stream_track_metrics.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_WEBRTC_MEDIA_STREAM_TRACK_METRICS_H_
 #define CONTENT_RENDERER_MEDIA_WEBRTC_MEDIA_STREAM_TRACK_METRICS_H_
 
 #include <stdint.h>
 
 #include "base/memory/scoped_vector.h"
 #include "base/threading/non_thread_safe.h"
 #include "content/common/content_export.h"
 #include "third_party/webrtc/api/peerconnectioninterface.h"
 
 namespace webrtc {
 class MediaStreamInterface;
-class MediaStreamTrackInterface;
 }
 
 namespace content {
 
 class MediaStreamTrackMetricsObserver;
 class RTCPeerConnectionHandler;
 
 // Responsible for observing the connected lifetimes of tracks going
 // over a PeerConnection, and sending messages to the browser process
 // about lifetime events.
@@ skipping 65 matching lines @@
 
   typedef ScopedVector<MediaStreamTrackMetricsObserver> ObserverVector;
   ObserverVector observers_;
 
   webrtc::PeerConnectionInterface::IceConnectionState ice_state_;
 };
 
 }  // namespace
 
 #endif  // CONTENT_RENDERER_MEDIA_WEBRTC_MEDIA_STREAM_TRACK_METRICS_H_