Implemented the GetSources() in native code.

webrtc/pc/channel.cc

Index: webrtc/pc/channel.cc
diff --git a/webrtc/pc/channel.cc b/webrtc/pc/channel.cc
index ecc1c9a633c6d4a935a146f048483256ccdc5d49..32c399c0770416ecaddff612ef402e37706e7f28 100644
--- a/webrtc/pc/channel.cc
+++ b/webrtc/pc/channel.cc
@@ -1663,6 +1663,13 @@ bool VoiceChannel::GetStats(VoiceMediaInfo* stats) {
                                             media_channel(), stats));
 }
 
+std::vector<webrtc::RtpContributingSource*>
+VoiceChannel::GetContributingSources(uint32_t ssrc) {
+  return worker_thread()->Invoke<std::vector<webrtc::RtpContributingSource*>>(
+      RTC_FROM_HERE,
+      Bind(&VoiceMediaChannel::GetContributingSources, media_channel(), ssrc));

[Zhi Huang, 2017/03/31 06:44:04]

I'll downcast this instead of adding the method to the basic class because there
would be circular dependency between the rtpreceiveritnerface.h and
mediachannel.h.

+}
+
 void VoiceChannel::StartMediaMonitor(int cms) {
   media_monitor_.reset(new VoiceMediaMonitor(media_channel(), worker_thread(),
       rtc::Thread::Current()));