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..d8a73362d317f762370b55544c0762df93b8a262 100644
--- a/webrtc/pc/channel.cc
+++ b/webrtc/pc/channel.cc
@@ -23,6 +23,7 @@
 #include "webrtc/base/trace_event.h"
 #include "webrtc/media/base/mediaconstants.h"
 #include "webrtc/media/base/rtputils.h"
+#include "webrtc/media/engine/webrtcvoiceengine.h"
 #include "webrtc/p2p/base/packettransportinternal.h"
 #include "webrtc/pc/channelmanager.h"
 
@@ -1663,6 +1664,14 @@ 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(&WebRtcVoiceMediaChannel::GetContributingSources,

[the sun, 2017/04/04 21:09:59]

Looking at the other methods, the pattern is to call via media_channel() here,
and add an overridable method on VoiceMediaChannel, instead of casting. However,
this is all subject for refactoring and I don't know the code that well, so
check with deadbeef@ or pthatcher@ if they're ok with the way you're doing it.

[Zhi Huang, 2017/04/05 04:16:04]

I didn't add the method to the base class because there would be a circular
dependency between mediachannel.h and rtpreceiverinterface.h

+           static_cast<WebRtcVoiceMediaChannel*>(media_channel()), ssrc));
+}
+
 void VoiceChannel::StartMediaMonitor(int cms) {
   media_monitor_.reset(new VoiceMediaMonitor(media_channel(), worker_thread(),
       rtc::Thread::Current()));