Forward the SignalFirstPacketReceived to RtpReceiver.

webrtc/api/rtpreceiverinterface.h

Index: webrtc/api/rtpreceiverinterface.h
diff --git a/webrtc/api/rtpreceiverinterface.h b/webrtc/api/rtpreceiverinterface.h
index ef4f0e113f36d297725e49ce17dcf530c0cdd3b3..e4c8cdccb9d57a7e3474d4b37fe1160650199516 100644
--- a/webrtc/api/rtpreceiverinterface.h
+++ b/webrtc/api/rtpreceiverinterface.h
@@ -20,9 +20,18 @@
 #include "webrtc/api/proxy.h"
 #include "webrtc/base/refcount.h"
 #include "webrtc/base/scoped_ref_ptr.h"
+#include "webrtc/pc/mediasession.h"
 
 namespace webrtc {
 
+class RtpReceiverObserverInterface {
+ public:
+  virtual void OnFirstPacketReceived(cricket::MediaType media_type) = 0;

[pthatcher1, 2016/06/08 17:35:55]

Should we just use the kind here instead of media_type?  That would be more
consistent for the API and make the tests more simple.

[Zhi Huang, 2016/06/09 00:37:36]

The hangouts team want this interface. Since I have added media_type() to the
Audio/VideoRtpReceiver, I think this should be fine.

+
+ protected:
+  virtual ~RtpReceiverObserverInterface() {}
+};
+
 class RtpReceiverInterface : public rtc::RefCountInterface {
  public:
   virtual rtc::scoped_refptr<MediaStreamTrackInterface> track() const = 0;
@@ -39,6 +48,8 @@ class RtpReceiverInterface : public rtc::RefCountInterface {
   virtual RtpParameters GetParameters() const = 0;
   virtual bool SetParameters(const RtpParameters& parameters) = 0;
 
+  virtual void SetObserver(RtpReceiverObserverInterface* observer) = 0;
+
  protected:
   virtual ~RtpReceiverInterface() {}
 };
@@ -50,6 +61,7 @@ PROXY_CONSTMETHOD0(std::string, id)
 PROXY_METHOD0(void, Stop)
 PROXY_CONSTMETHOD0(RtpParameters, GetParameters);
 PROXY_METHOD1(bool, SetParameters, const RtpParameters&)
+PROXY_METHOD1(void, SetObserver, RtpReceiverObserverInterface*);
 END_SIGNALING_PROXY()
 
 }  // namespace webrtc