Push back on the video encoder to avoid building queues in the pacer.

modules/congestion_controller/include/send_side_congestion_controller.h

Index: modules/congestion_controller/include/send_side_congestion_controller.h
diff --git a/modules/congestion_controller/include/send_side_congestion_controller.h b/modules/congestion_controller/include/send_side_congestion_controller.h
index 77bdf3784e7fe37d8206c9a127328228abb5e091..cb4b6410c98615a3c1fefdba7b5ceba5e1cef207 100644
--- a/modules/congestion_controller/include/send_side_congestion_controller.h
+++ b/modules/congestion_controller/include/send_side_congestion_controller.h
@@ -154,6 +154,9 @@ class SendSideCongestionController : public CallStatsObserver,
 
   rtc::RaceChecker worker_race_;
 
+  bool pacer_pushback_experiment_ = false;
+  float encoding_rate_ = 1.0;
+
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(SendSideCongestionController);
 };