Less lock acquisitions for AudioMixer.

webrtc/modules/audio_mixer/audio_mixer.h

Index: webrtc/modules/audio_mixer/audio_mixer.h
diff --git a/webrtc/modules/audio_mixer/audio_mixer.h b/webrtc/modules/audio_mixer/audio_mixer.h
index 080fc141d87e1d9ee82e563bf3ea9104b52e7c6e..6f0329b658d7bbc781dd7e0f91c200c4fac461cf 100644
--- a/webrtc/modules/audio_mixer/audio_mixer.h
+++ b/webrtc/modules/audio_mixer/audio_mixer.h
@@ -28,7 +28,6 @@ class AudioMixer {
     kWbInHz = 16000,
     kSwbInHz = 32000,
     kFbInHz = 48000,
-    kLowestPossible = -1,

[aleloi, 2016/08/30 15:13:33]

Not used any longer.

     kDefaultFrequency = kWbInHz
   };
 
@@ -70,6 +69,9 @@ class AudioMixer {
 
  protected:
   AudioMixer() {}
+
+ private:
+  RTC_DISALLOW_COPY_AND_ASSIGN(AudioMixer);

[aleloi, 2016/08/30 15:13:33]

Copying a mixer should be forbidden, as the mixer expects only it can
ask AudioSources for audio. There hasn't been any use case for
assignment.

 };
 }  // namespace webrtc