Forward the SignalFirstPacketReceived to RtpReceiver.

webrtc/api/mediastreamprovider.h

Index: webrtc/api/mediastreamprovider.h
diff --git a/webrtc/api/mediastreamprovider.h b/webrtc/api/mediastreamprovider.h
index b23e17bd4bb959a1bfd57a4f5f02c649945de471..ac1181c5ebdaabc8f95c1fd9aca55d9616e12c52 100644
--- a/webrtc/api/mediastreamprovider.h
+++ b/webrtc/api/mediastreamprovider.h
@@ -72,6 +72,9 @@ class AudioProviderInterface {
       uint32_t ssrc,
       const RtpParameters& parameters) = 0;
 
+  // Called when the first audio packet is received.
+  sigslot::signal0<> SignalFirstAudioPacketReceived;
+
  protected:
   virtual ~AudioProviderInterface() {}
 };
@@ -102,6 +105,9 @@ class VideoProviderInterface {
       uint32_t ssrc,
       const RtpParameters& parameters) = 0;
 
+  // Called when the first video packet is received.
+  sigslot::signal0<> SignalFirstVideoPacketReceived;
+
  protected:
   virtual ~VideoProviderInterface() {}
 };