Support external audio mixer.

webrtc/api/peerconnection.h

Index: webrtc/api/peerconnection.h
diff --git a/webrtc/api/peerconnection.h b/webrtc/api/peerconnection.h
index 70fd86779f538ad07df0308c65c08cfbacd2ab22..6d49e360debe864cb53bea418b29c19af0b0a6aa 100644
--- a/webrtc/api/peerconnection.h
+++ b/webrtc/api/peerconnection.h
@@ -145,6 +145,7 @@ class PeerConnection : public PeerConnectionInterface,
   void Close() override;
 
   sigslot::signal1<DataChannel*> SignalDataChannelCreated;
+  std::vector<uint32_t> GetRemoteAudioTrackSsrcs() override;

[aleloi, 2016/12/05 14:03:08]

Is there problems with implementing this in client-code through a
PeerConnectionObserver instead?

[GeorgeZ, 2016/12/05 17:56:18]

Functions in PeerConnectionObserver are event/callbacks functions to response
the state changes of Peerconnection. GetRemoteAudioTrackSsrcs() is more a state
inquire/get function and not fit in the event/callback function category. Since
PeerconnectionInterface has many get functions, I guess it may be a better place
to put GetRemoteAudioTrackSsrcs() into.

 
   // Virtual for unit tests.
   virtual const std::vector<rtc::scoped_refptr<DataChannel>>&