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 b508c39f7e0289e3fb3c79eac3491275c0022662..784a95423dc9afe423d90c94184b70e9c7de4161 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() {}
 };
@@ -105,6 +108,9 @@ class VideoProviderInterface {
       uint32_t ssrc,
       const RtpParameters& parameters) = 0;
 
+  // Called when the first video packet is received.
+  sigslot::signal0<> SignalFirstVideoPacketReceived;
+
  protected:
   virtual ~VideoProviderInterface() {}
 };