Prioritize video packets when sending padding or preemptive retransmits.

webrtc/modules/pacing/packet_router.cc

Index: webrtc/modules/pacing/packet_router.cc
diff --git a/webrtc/modules/pacing/packet_router.cc b/webrtc/modules/pacing/packet_router.cc
index af1d5595be9193f491058ab3b179a9161cfd5bec..65d6db7cb704015cb6dac0fa2e6f309fe93f8440 100644
--- a/webrtc/modules/pacing/packet_router.cc
+++ b/webrtc/modules/pacing/packet_router.cc
@@ -30,7 +30,13 @@ void PacketRouter::AddRtpModule(RtpRtcp* rtp_module) {
   rtc::CritScope cs(&modules_crit_);
   RTC_DCHECK(std::find(rtp_modules_.begin(), rtp_modules_.end(), rtp_module) ==
              rtp_modules_.end());
-  rtp_modules_.push_back(rtp_module);
+  // Put modules which can use regular payload packets (over rtx) instead of
+  // padding first as it's less of a waste
+  if ((rtp_module->RtxSendStatus() & kRtxRedundantPayloads) > 0) {
+    rtp_modules_.push_front(rtp_module);
+  } else {
+    rtp_modules_.push_back(rtp_module);
+  }
 }
 
 void PacketRouter::RemoveRtpModule(RtpRtcp* rtp_module) {
@@ -64,6 +70,7 @@ size_t PacketRouter::TimeToSendPadding(size_t bytes_to_send,
   RTC_DCHECK(pacer_thread_checker_.CalledOnValidThread());
   size_t total_bytes_sent = 0;
   rtc::CritScope cs(&modules_crit_);
+  // Rtp modules are ordered by which stream can most benefit from padding.
   for (RtpRtcp* module : rtp_modules_) {
     if (module->SendingMedia()) {
       size_t bytes_sent = module->TimeToSendPadding(