Elimiteted race condition in the AudioMixer.

webrtc/modules/audio_mixer/audio_mixer_impl.h

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 39 matching lines @@
   static rtc::scoped_refptr<AudioMixerImpl> Create();
 
   ~AudioMixerImpl() override;
 
   // AudioMixer functions
   bool AddSource(Source* audio_source) override;
   bool RemoveSource(Source* audio_source) override;
 
   void Mix(int sample_rate_hz,
            size_t number_of_channels,
-           AudioFrame* audio_frame_for_mixing) override;
+           AudioFrame* audio_frame_for_mixing) override LOCKS_EXCLUDED(crit_);
 
   // Returns true if the source was mixed last round. Returns
   // false and logs an error if the source was never added to the
   // mixer.
   bool GetAudioSourceMixabilityStatusForTest(Source* audio_source) const;
 
  protected:
   explicit AudioMixerImpl(std::unique_ptr<AudioProcessing> limiter);
 
  private:
@@ skipping 35 matching lines @@
   uint32_t time_stamp_ GUARDED_BY(race_checker_);
 
   // Used for inhibiting saturation in mixing.
   std::unique_ptr<AudioProcessing> limiter_ GUARDED_BY(race_checker_);
 
   RTC_DISALLOW_COPY_AND_ASSIGN(AudioMixerImpl);
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_IMPL_H_