Make FlexFEC packets paceable through RTPSender.

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index 15fb3255757cb362a4b958623052bb6a58eaef97..19bc862a78482b1cdd1f975f0c933eb303d941f3 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -229,6 +229,10 @@ void ModuleRtpRtcpImpl::SetRtxSendPayloadType(int payload_type,
   rtp_sender_.SetRtxPayloadType(payload_type, associated_payload_type);
 }
 
+rtc::Optional<uint32_t> ModuleRtpRtcpImpl::FlexfecSsrc() const {
+  return rtp_sender_.FlexfecSsrc();
+}
+
 int32_t ModuleRtpRtcpImpl::IncomingRtcpPacket(
     const uint8_t* rtcp_packet,
     const size_t length) {
@@ -400,8 +404,13 @@ bool ModuleRtpRtcpImpl::TimeToSendPacket(uint32_t ssrc,
                                          int64_t capture_time_ms,
                                          bool retransmission,
                                          int probe_cluster_id) {
-  if (SendingMedia() && ssrc == rtp_sender_.SSRC()) {
-    return rtp_sender_.TimeToSendPacket(sequence_number, capture_time_ms,
+  if (!SendingMedia()) {
+    return true;
+  }
+  uint32_t media_ssrc = rtp_sender_.SSRC();
+  rtc::Optional<uint32_t> flexfec_ssrc = rtp_sender_.FlexfecSsrc();
+  if (ssrc == media_ssrc || (flexfec_ssrc && ssrc == flexfec_ssrc)) {
+    return rtp_sender_.TimeToSendPacket(ssrc, sequence_number, capture_time_ms,
                                         retransmission, probe_cluster_id);
   }
   // No RTP sender is interested in sending this packet.