Cast: cancel re-sending if a later nack packet says the receiver doesn't want it anymore

media/cast/transport/pacing/paced_sender.cc

Index: media/cast/transport/pacing/paced_sender.cc
diff --git a/media/cast/transport/pacing/paced_sender.cc b/media/cast/transport/pacing/paced_sender.cc
index a401817ae8f7cf30b535ee3a7aa71a5c821a3e56..10b42240759a3fd2c2580f802a7ed3b1e8b473ea 100644
--- a/media/cast/transport/pacing/paced_sender.cc
+++ b/media/cast/transport/pacing/paced_sender.cc
@@ -104,6 +104,10 @@ bool PacedSender::SendRtcpPacket(uint32 ssrc, PacketRef packet) {
   return true;
 }
 
+void PacedSender::CancelSendingPacket(const PacketKey& packet_key) {
+  packet_list_.erase(packet_key);
+}
+
 PacketRef PacedSender::GetNextPacket(PacketType* packet_type) {
   std::map<PacketKey, std::pair<PacketType, PacketRef> >::iterator i;
   i = packet_list_.begin();