Implemented the GetSources() in native code.

webrtc/media/engine/webrtcvoiceengine.cc

 /*
  *  Copyright (c) 2004 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 1563 matching lines @@
     if (playout) {
       LOG(LS_INFO) << "Starting playout for channel #" << channel();
       stream_->Start();
     } else {
       LOG(LS_INFO) << "Stopping playout for channel #" << channel();
       stream_->Stop();
     }
     playout_ = playout;
   }
 
+  std::vector<webrtc::RtpSource> GetSources() {
+    RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
+    RTC_DCHECK(stream_);
+    return stream_->GetSources();
+  }
+
  private:
   void RecreateAudioReceiveStream() {
     RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
     if (stream_) {
       call_->DestroyAudioReceiveStream(stream_);
     }
     stream_ = call_->CreateAudioReceiveStream(config_);
     RTC_CHECK(stream_);
     SetPlayout(playout_);
   }
@@ skipping 999 matching lines @@
     return;
   }
   const auto it = recv_streams_.find(ssrc);
   if (it == recv_streams_.end()) {
     LOG(LS_WARNING) << "SetRawAudioSink: no recv stream " << ssrc;
     return;
   }
   it->second->SetRawAudioSink(std::move(sink));
 }
 
+std::vector<webrtc::RtpSource> WebRtcVoiceMediaChannel::GetSources(
+    uint32_t ssrc) const {
+  auto it = recv_streams_.find(ssrc);
+  RTC_DCHECK(it != recv_streams_.end())
+      << "Attempting to get contributing sources for SSRC:" << ssrc
+      << " which doesn't exist.";
+  return it->second->GetSources();
+}
+
 int WebRtcVoiceMediaChannel::GetReceiveChannelId(uint32_t ssrc) const {
   RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   const auto it = recv_streams_.find(ssrc);
   if (it != recv_streams_.end()) {
     return it->second->channel();
   }
   return -1;
 }
 
 int WebRtcVoiceMediaChannel::GetSendChannelId(uint32_t ssrc) const {
@@ skipping 13 matching lines @@
                       ssrc);
   if (it != unsignaled_recv_ssrcs_.end()) {
     unsignaled_recv_ssrcs_.erase(it);
     return true;
   }
   return false;
 }
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VOICE