Reland of Implemented the GetSources() in native code.

webrtc/api/test/mock_rtpreceiver.h

Index: webrtc/api/test/mock_rtpreceiver.h
diff --git a/webrtc/api/test/mock_rtpreceiver.h b/webrtc/api/test/mock_rtpreceiver.h
index 25f5c28caa62b3ac2c70121a750b5a0ca9a94cad..552a653100cf2d3f44b320ecd0bc8440cd4bf3a8 100644
--- a/webrtc/api/test/mock_rtpreceiver.h
+++ b/webrtc/api/test/mock_rtpreceiver.h
@@ -12,6 +12,7 @@
 #define WEBRTC_API_TEST_MOCK_RTPRECEIVER_H_
 
 #include <string>
+#include <vector>
 
 #include "webrtc/api/rtpreceiverinterface.h"
 #include "webrtc/test/gmock.h"
@@ -27,6 +28,7 @@
   MOCK_CONST_METHOD0(GetParameters, RtpParameters());
   MOCK_METHOD1(SetParameters, bool(const RtpParameters&));
   MOCK_METHOD1(SetObserver, void(RtpReceiverObserverInterface*));
+  MOCK_CONST_METHOD0(GetSources, std::vector<RtpSource>());
 };
 
 }  // namespace webrtc