Add sending Nack to RtcpTransceiver

Bug: webrtc:8239
Change-Id: Idf27bb05958d9eceaf601078019f05444232581f
Reviewed-on: https://webrtc-review.googlesource.com/26260
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20907}
diff --git a/modules/rtp_rtcp/source/rtcp_transceiver.h b/modules/rtp_rtcp/source/rtcp_transceiver.h
index 9d69545..417943a 100644
--- a/modules/rtp_rtcp/source/rtcp_transceiver.h
+++ b/modules/rtp_rtcp/source/rtcp_transceiver.h
@@ -44,7 +44,10 @@
   // Stops sending REMB in following compound packets.
   void UnsetRemb();
 
-  // Request new key frame.
+  // Reports missing packets, https://tools.ietf.org/html/rfc4585#section-6.2.1
+  void SendNack(uint32_t ssrc, std::vector<uint16_t> sequence_numbers);
+
+  // Requests new key frame.
   // using PLI, https://tools.ietf.org/html/rfc4585#section-6.3.1.1
   void SendPictureLossIndication(std::vector<uint32_t> ssrcs);
   // using FIR, https://tools.ietf.org/html/rfc5104#section-4.3.1.2