Use RaceChecker instead of ThreadChecker in a few places.

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 871ba0fcec984b99d7696a498e21b967bd2d5b8a..d5fd8b98d2f4a65d4d54fa1e1f448562e9ff74b3 100644
--- a/webrtc/modules/pacing/packet_router.cc
+++ b/webrtc/modules/pacing/packet_router.cc
@@ -22,9 +22,7 @@ namespace webrtc {
 PacketRouter::PacketRouter()
     : last_remb_time_ms_(rtc::TimeMillis()),
       last_send_bitrate_bps_(0),
-      transport_seq_(0) {
-  pacer_thread_checker_.DetachFromThread();
-}
+      transport_seq_(0) {}
 
 PacketRouter::~PacketRouter() {
   RTC_DCHECK(rtp_send_modules_.empty());
@@ -98,7 +96,7 @@ bool PacketRouter::TimeToSendPacket(uint32_t ssrc,
                                     int64_t capture_timestamp,
                                     bool retransmission,
                                     const PacedPacketInfo& pacing_info) {
-  RTC_DCHECK(pacer_thread_checker_.CalledOnValidThread());
+  RTC_DCHECK_RUNS_SERIALIZED(&pacer_race_);
   rtc::CritScope cs(&modules_crit_);
   for (auto* rtp_module : rtp_send_modules_) {
     if (!rtp_module->SendingMedia())
@@ -114,7 +112,7 @@ bool PacketRouter::TimeToSendPacket(uint32_t ssrc,
 
 size_t PacketRouter::TimeToSendPadding(size_t bytes_to_send,
                                        const PacedPacketInfo& pacing_info) {
-  RTC_DCHECK(pacer_thread_checker_.CalledOnValidThread());
+  RTC_DCHECK_RUNS_SERIALIZED(&pacer_race_);
   size_t total_bytes_sent = 0;
   rtc::CritScope cs(&modules_crit_);
   // Rtp modules are ordered by which stream can most benefit from padding.
@@ -208,7 +206,7 @@ bool PacketRouter::SendRemb(uint32_t bitrate_bps,
 }
 
 bool PacketRouter::SendTransportFeedback(rtcp::TransportFeedback* packet) {
-  RTC_DCHECK(pacer_thread_checker_.CalledOnValidThread());
+  RTC_DCHECK_RUNS_SERIALIZED(&pacer_race_);
   rtc::CritScope cs(&modules_crit_);
   // Prefer send modules.
   for (auto* rtp_module : rtp_send_modules_) {