remove the race related to output_delay_ms_ in ADM and races in the unittests.

content/renderer/media/webrtc_audio_device_impl.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 CONTENT_RENDERER_MEDIA_WEBRTC_AUDIO_DEVICE_IMPL_H_
 #define CONTENT_RENDERER_MEDIA_WEBRTC_AUDIO_DEVICE_IMPL_H_
 #pragma once
 
 #include <vector>
 
@@ skipping 303 matching lines @@
   scoped_array<int16> output_buffer_;
 
   webrtc::AudioDeviceModule::ErrorCode last_error_;
 
   base::TimeTicks last_process_time_;
 
   // Id of the media session to be started, it tells which device to be used
   // on the input/capture side.
   int session_id_;
 
-  // Protects |recording_|.
-  base::Lock lock_;
+  // Protects |recording_|, |output_delay_ms_|.
+  mutable base::Lock lock_;
 
   int bytes_per_sample_;
 
   bool initialized_;
   bool playing_;
   bool recording_;
 
   DISALLOW_COPY_AND_ASSIGN(WebRtcAudioDeviceImpl);
 };
 
 #endif  // CONTENT_RENDERER_MEDIA_WEBRTC_AUDIO_DEVICE_IMPL_H_