Implemented the GetSources() in native code.

webrtc/pc/rtpreceiver.h

 /*
  *  Copyright 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 70 matching lines @@
   // RtpReceiverInternal implementation.
   void Stop() override;
   uint32_t ssrc() const override { return ssrc_; }
 
   void SetObserver(RtpReceiverObserverInterface* observer) override;
 
   // Does not take ownership.
   // Should call SetChannel(nullptr) before |channel| is destroyed.
   void SetChannel(cricket::VoiceChannel* channel);
 
+  std::vector<RtpSource> GetSources() const override;
+
  private:
   void Reconfigure();
   void OnFirstPacketReceived(cricket::BaseChannel* channel);
 
   const std::string id_;
   const uint32_t ssrc_;
   cricket::VoiceChannel* channel_;
   const rtc::scoped_refptr<AudioTrackInterface> track_;
   bool cached_track_enabled_;
   double cached_volume_ = 1;
@@ skipping 57 matching lines @@
   rtc::scoped_refptr<VideoTrackSource> source_;
   rtc::scoped_refptr<VideoTrackInterface> track_;
   bool stopped_ = false;
   RtpReceiverObserverInterface* observer_ = nullptr;
   bool received_first_packet_ = false;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_PC_RTPRECEIVER_H_