Mark |Clock*| as |const Clock*| (for some CongestionController and BWE related modules)

webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h

Index: webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h
index f88a2fc0329c4cfad1f6914be0e6dc6c6edc6c61..08f63e2150f8717d262a78c0386969738c4e6594 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h
+++ b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h
@@ -69,7 +69,7 @@ struct Cluster {
 class RemoteBitrateEstimatorAbsSendTime : public RemoteBitrateEstimator {
  public:
   RemoteBitrateEstimatorAbsSendTime(RemoteBitrateObserver* observer,
-                                    Clock* clock);
+                                    const Clock* clock);
   virtual ~RemoteBitrateEstimatorAbsSendTime() {}
 
   void IncomingPacket(int64_t arrival_time_ms,
@@ -115,7 +115,7 @@ class RemoteBitrateEstimatorAbsSendTime : public RemoteBitrateEstimator {
   void TimeoutStreams(int64_t now_ms) EXCLUSIVE_LOCKS_REQUIRED(&crit_);
 
   rtc::ThreadChecker network_thread_;
-  Clock* const clock_;
+  const Clock* const clock_;
   RemoteBitrateObserver* const observer_;
   std::unique_ptr<InterArrival> inter_arrival_;
   std::unique_ptr<OveruseEstimator> estimator_;