Forward the SignalFirstPacketReceived to RtpReceiver.

webrtc/api/webrtcsession.h

Index: webrtc/api/webrtcsession.h
diff --git a/webrtc/api/webrtcsession.h b/webrtc/api/webrtcsession.h
index 9ba7605e67d60e4a44b101032f4e229b05568cbf..76af6c7c3d2669830665c77731d3dfd0e661651d 100644
--- a/webrtc/api/webrtcsession.h
+++ b/webrtc/api/webrtcsession.h
@@ -310,6 +310,8 @@ class WebRtcSession : public AudioProviderInterface,
   void OnCertificateReady(
       const rtc::scoped_refptr<rtc::RTCCertificate>& certificate);
   void OnDtlsSetupFailure(cricket::BaseChannel*, bool rtcp);
+  // Called when the channel received the first packet.
+  void OnChannelFirstPacketReceived(cricket::BaseChannel*);
 
   // For unit test.
   bool waiting_for_certificate_for_testing() const;
@@ -527,6 +529,9 @@ class WebRtcSession : public AudioProviderInterface,
   // Declares the RTCP mux policy for the WebRTCSession.
   PeerConnectionInterface::RtcpMuxPolicy rtcp_mux_policy_;
 
+  bool received_first_video_packet_ = false;
+  bool received_first_audio_packet_ = false;
+
   RTC_DISALLOW_COPY_AND_ASSIGN(WebRtcSession);
 };
 }  // namespace webrtc