Implemented the GetSources() in native code.

webrtc/voice_engine/channel_proxy.cc

 /*
  *  Copyright (c) 2015 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 373 matching lines @@
   // See: https://bugs.chromium.org/p/webrtc/issues/detail?id=7405
   // RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   channel()->OnRecoverableUplinkPacketLossRate(recoverable_packet_loss_rate);
 }
 
 void ChannelProxy::RegisterLegacyReceiveCodecs() {
   RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   channel()->RegisterLegacyReceiveCodecs();
 }
 
+const std::vector<RtpContributingSource*>&
+ChannelProxy::GetContributingSources() {
+  return channel()->GetContributingSources();
+}
+
 Channel* ChannelProxy::channel() const {
   RTC_DCHECK(channel_owner_.channel());
   return channel_owner_.channel();
 }
 
 }  // namespace voe
 }  // namespace webrtc