Implemented the GetSources() in native code.

webrtc/modules/rtp_rtcp/include/rtp_receiver.h

 /*
  *  Copyright (c) 2012 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_MODULES_RTP_RTCP_INCLUDE_RTP_RECEIVER_H_
 #define WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RECEIVER_H_
 
+#include <vector>
+
+#include "webrtc/api/rtpreceiverinterface.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
 struct CodecInst;
 class RTPPayloadRegistry;
 class VideoCodec;
 
+class RtpContributingSource : public RtpContributingSourceInterface {
+ public:
+  RtpContributingSource() : timestamp_(0), source_(0) {}
+
+  explicit RtpContributingSource(int64_t timestamp, uint32_t source)
+      : timestamp_(timestamp), source_(source) {}
+
+  int64_t timestamp() const override { return timestamp_; }
+
+  uint32_t source() const override { return source_; }
+
+  // Always return 0 in the current implementation.
+  // TODO(zhihuang): Implement this method to return real audio level.
+  int8_t audio_level() const override { return 0; }

[hbos, 2017/03/30 09:51:54]

Return a value that doesn't map to a meaningful value, say -1 or
rtc::Optional<>()

[Zhi Huang, 2017/03/31 06:44:04]

Done.

+
+  void set_timestamp(int64_t timestamp) { timestamp_ = timestamp; }
+
+ private:
+  int64_t timestamp_;
+  uint32_t source_;
+};
+
 class TelephoneEventHandler {
  public:
   virtual ~TelephoneEventHandler() {}
 
   // The following three methods implement the TelephoneEventHandler interface.
   // Forward DTMFs to decoder for playout.
   virtual void SetTelephoneEventForwardToDecoder(bool forward_to_decoder) = 0;
 
   // Is forwarding of outband telephone events turned on/off?
   virtual bool TelephoneEventForwardToDecoder() const = 0;
@@ skipping 49 matching lines @@
   virtual bool LastReceivedTimeMs(int64_t* receive_time_ms) const = 0;
 
   // Returns the remote SSRC of the currently received RTP stream.
   virtual uint32_t SSRC() const = 0;
 
   // Returns the current remote CSRCs.
   virtual int32_t CSRCs(uint32_t array_of_csrc[kRtpCsrcSize]) const = 0;
 
   // Returns the current energy of the RTP stream received.
   virtual int32_t Energy(uint8_t array_of_energy[kRtpCsrcSize]) const = 0;
+
+  virtual const std::vector<RtpContributingSource*>&
+  GetContributingSources() = 0;
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RECEIVER_H_