Remove hardcoded kValueSizeBytes values from variable-length header extensions.

webrtc/modules/congestion_controller/delay_based_bwe.h

Index: webrtc/modules/congestion_controller/delay_based_bwe.h
diff --git a/webrtc/modules/congestion_controller/delay_based_bwe.h b/webrtc/modules/congestion_controller/delay_based_bwe.h
index c44ea12e1c752479f20fa3798d0f9436823918bd..a2c182d0f81ab6cb73deef088b832670edab4b2f 100644
--- a/webrtc/modules/congestion_controller/delay_based_bwe.h
+++ b/webrtc/modules/congestion_controller/delay_based_bwe.h
@@ -17,7 +17,7 @@
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/constructormagic.h"
-#include "webrtc/base/thread_checker.h"
+#include "webrtc/base/race_checker.h"
 #include "webrtc/modules/congestion_controller/median_slope_estimator.h"
 #include "webrtc/modules/congestion_controller/probe_bitrate_estimator.h"
 #include "webrtc/modules/congestion_controller/trendline_estimator.h"
@@ -70,7 +70,7 @@ class DelayBasedBwe {
                       bool overusing,
                       uint32_t* target_bitrate_bps);
 
-  rtc::ThreadChecker network_thread_;
+  rtc::RaceChecker race_checker_;
   RtcEventLog* const event_log_;
   const Clock* const clock_;
   std::unique_ptr<InterArrival> inter_arrival_;