Implement timing frames.

webrtc/modules/rtp_rtcp/source/rtp_sender.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_sender.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_sender.cc b/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
index e0c10e9114148b6a9c30cd7e0f9c67945eb3533a..2f1e1b435be58c6d16c1b5a052723dc8bd54401a 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
@@ -741,6 +741,9 @@ bool RTPSender::PrepareAndSendPacket(std::unique_ptr<RtpPacketToSend> packet,
                                                    diff_ms);
   packet_to_send->SetExtension<AbsoluteSendTime>(now_ms);
 
+  if (packet->HasExtension<VideoTimingExtension>())
+    packet->set_pacer_exit_time_ms(clock_->TimeInMilliseconds());
+
   PacketOptions options;
   if (UpdateTransportSequenceNumber(packet_to_send, &options.packet_id)) {
     AddPacketToTransportFeedback(options.packet_id, *packet_to_send,