Translate loss notifications and pass to encoder

Translate LossNotification RTCP messages (sequence number to
timestamp and additional information), then send the translted
message onwards to the encoder.

Bug: webrtc:10501
Change-Id: If2fd943f75c36cf813a83120318d8eefc8c595d2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/131950
Commit-Queue: Elad Alon <eladalon@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27545}
diff --git a/api/video/video_stream_encoder_interface.h b/api/video/video_stream_encoder_interface.h
index 5463118..4e3c470 100644
--- a/api/video/video_stream_encoder_interface.h
+++ b/api/video/video_stream_encoder_interface.h
@@ -78,6 +78,10 @@
   // Request a key frame. Used for signalling from the remote receiver.
   virtual void SendKeyFrame() = 0;
 
+  // Inform the encoder that a loss has occurred.
+  virtual void OnLossNotification(
+      const VideoEncoder::LossNotification& loss_notification) = 0;
+
   // Set the currently estimated network properties. A |target_bitrate|
   // of zero pauses the encoder.
   // |link_allocation| is the bandwidth available for this video stream on the