Made AudioReceiveStream a mixer participant.

webrtc/voice_engine/channel_proxy.h

Index: webrtc/voice_engine/channel_proxy.h
diff --git a/webrtc/voice_engine/channel_proxy.h b/webrtc/voice_engine/channel_proxy.h
index 1d0116d969d8cbfe3dbb7e990110e01f2d876c0a..45c0fab8673a076eff1c0fe3410056f842c8da47 100644
--- a/webrtc/voice_engine/channel_proxy.h
+++ b/webrtc/voice_engine/channel_proxy.h
@@ -11,6 +11,7 @@
 #ifndef WEBRTC_VOICE_ENGINE_CHANNEL_PROXY_H_
 #define WEBRTC_VOICE_ENGINE_CHANNEL_PROXY_H_
 
+#include "webrtc/api/audio/audio_mixer.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/thread_checker.h"
 #include "webrtc/voice_engine/channel_manager.h"
@@ -94,10 +95,14 @@ class ChannelProxy {
 
   virtual void SetRtcpRttStats(RtcpRttStats* rtcp_rtt_stats);
 
+  virtual AudioMixer::Source::AudioFrameWithInfo GetAudioFrameWithInfo(
+      int sample_rate_hz);
+
  private:
   Channel* channel() const;
 
   rtc::ThreadChecker thread_checker_;
+  rtc::ThreadChecker mixer_callback_thread_checker_;

[the sun, 2016/10/13 12:16:56]

Use an rtc::RaceChecker here instead, and use i.e.
RTC_DCHECK_RUNS_SERIALIZED(audio_render_race_checker_) in the .cc

The reason is there are situations when both the calling capture and render
threads may change and "ownership" of the WebRTC resource is passed on. What we
do want to ensure is non-concurrent access - not necessarily lock to a single
thread *ever* calling these methods.

[aleloi, 2016/10/13 13:34:56]

Then I had an incorrect understanding of the threading model. I thought
previously that AudioMixer::Mix is called from a single thread. With this
assumption I "simplified" the locking scheme in the mixer. When the assumption
turned out to be not entirely correct (two threads asked for audio in Android
OpenSL ES, some tests restarted their audio poll thread) I changed the tests and
asked henrika@ to update OpenSL ES.

This means that a race checker will have to be added to AudioMixerImpl as well.
Depending on the difference between a thread checker and a race checker, locks
may have to be re-introduced to the mixer.

[the sun, 2016/10/13 13:51:33]

Acknowledged.

   ChannelOwner channel_owner_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(ChannelProxy);