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 98217bff266a2a67e7fbb99964210051d88fa5a1..4ad9874d4a710f9ea88d019671fa6ae75bd8a178 100644
--- a/webrtc/api/webrtcsession.h
+++ b/webrtc/api/webrtcsession.h
@@ -311,6 +311,8 @@ 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;
@@ -528,6 +530,9 @@ class WebRtcSession : public AudioProviderInterface,
   // Declares the RTCP mux policy for the WebRTCSession.
   PeerConnectionInterface::RtcpMuxPolicy rtcp_mux_policy_;
 
+  bool has_received_video_packet_ = false;
+  bool has_received_audio_packet_ = false;
+
   RTC_DISALLOW_COPY_AND_ASSIGN(WebRtcSession);
 };
 }  // namespace webrtc