Implemented the GetSources() in native code.

webrtc/modules/rtp_rtcp/include/rtp_receiver.h

Index: webrtc/modules/rtp_rtcp/include/rtp_receiver.h
diff --git a/webrtc/modules/rtp_rtcp/include/rtp_receiver.h b/webrtc/modules/rtp_rtcp/include/rtp_receiver.h
index 54a99c93a1de5fc4dbb62a08536d529242ca9572..95bade62fe638e7217c30e174388388c94290aa6 100644
--- a/webrtc/modules/rtp_rtcp/include/rtp_receiver.h
+++ b/webrtc/modules/rtp_rtcp/include/rtp_receiver.h
@@ -11,6 +11,9 @@
 #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"
 
@@ -89,6 +92,8 @@ class RtpReceiver {
 
   // Returns the current energy of the RTP stream received.
   virtual int32_t Energy(uint8_t array_of_energy[kRtpCsrcSize]) const = 0;
+
+  virtual std::vector<RtpSource> GetSources() const = 0;
 };
 }  // namespace webrtc