Reland of Implemented the GetSources() in native code.

webrtc/media/engine/fakewebrtccall.h

Index: webrtc/media/engine/fakewebrtccall.h
diff --git a/webrtc/media/engine/fakewebrtccall.h b/webrtc/media/engine/fakewebrtccall.h
index 6b2542245e7e88eb22cf84d5da1831d344192043..1ddf95ae15c0487c7c6eb5d1f61e5b9d8ffb233e 100644
--- a/webrtc/media/engine/fakewebrtccall.h
+++ b/webrtc/media/engine/fakewebrtccall.h
@@ -97,6 +97,9 @@
   int GetOutputLevel() const override { return 0; }
   void SetSink(std::unique_ptr<webrtc::AudioSinkInterface> sink) override;
   void SetGain(float gain) override;
+  std::vector<webrtc::RtpSource> GetSources() const override {
+    return std::vector<webrtc::RtpSource>();
+  }
 
   int id_ = -1;
   webrtc::AudioReceiveStream::Config config_;