Calculate the signal level on the media stream local audio track

content/renderer/media/webrtc_local_audio_track.h

 // Copyright 2013 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_LOCAL_AUDIO_TRACK_H_
 #define CONTENT_RENDERER_MEDIA_WEBRTC_LOCAL_AUDIO_TRACK_H_
 
 #include <list>
 #include <string>
 
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "content/renderer/media/media_stream_track.h"
 #include "content/renderer/media/tagged_list.h"
 #include "content/renderer/media/webrtc_audio_device_impl.h"
 #include "content/renderer/media/webrtc_local_audio_source_provider.h"
 
 namespace content {
 
+class MediaStreamAudioLevelCalculator;
 class MediaStreamAudioSink;
 class MediaStreamAudioSinkOwner;
 class MediaStreamAudioTrackSink;
 class PeerConnectionAudioSink;
 class WebAudioCapturerSource;
 class WebRtcAudioCapturer;
 class WebRtcLocalAudioTrackAdapter;
 
 // A WebRtcLocalAudioTrack instance contains the implementations of
 // MediaStreamTrackExtraData.
@@ skipping 78 matching lines @@
   mutable base::Lock lock_;
 
   // Audio parameters of the audio capture stream.
   // Accessed on only the audio capture thread.
   media::AudioParameters audio_parameters_;
 
   // The source provider to feed the track data to other clients like
   // WebAudio.
   scoped_ptr<WebRtcLocalAudioSourceProvider> source_provider_;
 
+  // Used to calculate the signal level that shows in the UI.
+  // Accessed on only the audio thread.
+  scoped_ptr<MediaStreamAudioLevelCalculator> level_calculator_;
+
   DISALLOW_COPY_AND_ASSIGN(WebRtcLocalAudioTrack);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_WEBRTC_LOCAL_AUDIO_TRACK_H_