Changed mixing to be done at the minimal possible frequency.

webrtc/modules/audio_mixer/audio_mixer_impl.h

Index: webrtc/modules/audio_mixer/audio_mixer_impl.h
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.h b/webrtc/modules/audio_mixer/audio_mixer_impl.h
index e2f55fce400ae76dae5d301e8cd1c26103ee9900..ec2989e55476adc8780ac6245055c2192943e842 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.h
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.h
@@ -55,8 +55,7 @@ class AudioMixerImpl : public AudioMixer {
   bool AddSource(Source* audio_source) override;
   bool RemoveSource(Source* audio_source) override;
 
-  void Mix(int sample_rate_hz,
-           size_t number_of_channels,
+  void Mix(size_t number_of_channels,
            AudioFrame* audio_frame_for_mixing) override LOCKS_EXCLUDED(crit_);
 
   // Returns true if the source was mixed last round. Returns