Implemented the GetSources() in native code.

webrtc/audio/audio_receive_stream.h

 /*
  *  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.
  */
 
 #ifndef WEBRTC_AUDIO_AUDIO_RECEIVE_STREAM_H_
 #define WEBRTC_AUDIO_AUDIO_RECEIVE_STREAM_H_
 
 #include <memory>
+#include <vector>
 
 #include "webrtc/api/audio/audio_mixer.h"
 #include "webrtc/audio/audio_state.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/thread_checker.h"
 #include "webrtc/call/audio_receive_stream.h"
 #include "webrtc/call/syncable.h"
 
 namespace webrtc {
 class PacketRouter;
 class RtcEventLog;
+class RtpContributingSource;
 class RtpPacketReceived;
 
 namespace voe {
 class ChannelProxy;
 }  // namespace voe
 
 namespace internal {
 class AudioSendStream;
 
 class AudioReceiveStream final : public webrtc::AudioReceiveStream,
                                  public AudioMixer::Source,
                                  public Syncable {
  public:
   AudioReceiveStream(PacketRouter* packet_router,
                      const webrtc::AudioReceiveStream::Config& config,
                      const rtc::scoped_refptr<webrtc::AudioState>& audio_state,
                      webrtc::RtcEventLog* event_log);
   ~AudioReceiveStream() override;
 
   // webrtc::AudioReceiveStream implementation.
   void Start() override;
   void Stop() override;
   webrtc::AudioReceiveStream::Stats GetStats() const override;
   int GetOutputLevel() const override;
   void SetSink(std::unique_ptr<AudioSinkInterface> sink) override;
   void SetGain(float gain) override;
+  const std::vector<RtpContributingSource*>& GetContributingSources() override;
 
   // TODO(nisse): Intended to be part of an RtpPacketReceiver interface.
   void OnRtpPacket(const RtpPacketReceived& packet);
 
   // AudioMixer::Source
   AudioFrameInfo GetAudioFrameWithInfo(int sample_rate_hz,
                                        AudioFrame* audio_frame) override;
   int Ssrc() const override;
   int PreferredSampleRate() const override;
 
@@ skipping 20 matching lines @@
   std::unique_ptr<voe::ChannelProxy> channel_proxy_;
 
   bool playing_ ACCESS_ON(worker_thread_checker_) = false;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(AudioReceiveStream);
 };
 }  // namespace internal
 }  // namespace webrtc
 
 #endif  // WEBRTC_AUDIO_AUDIO_RECEIVE_STREAM_H_