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

webrtc/modules/remote_bitrate_estimator/send_time_history.cc

Index: webrtc/modules/remote_bitrate_estimator/send_time_history.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/send_time_history.cc b/webrtc/modules/remote_bitrate_estimator/send_time_history.cc
index 9937234231452cbdd86a8c863b4126ab832c12ac..1c5ca12f5afadf34be43a9f3ee42eb3ed940208e 100644
--- a/webrtc/modules/remote_bitrate_estimator/send_time_history.cc
+++ b/webrtc/modules/remote_bitrate_estimator/send_time_history.cc
@@ -16,7 +16,8 @@
 
 namespace webrtc {
 
-SendTimeHistory::SendTimeHistory(Clock* clock, int64_t packet_age_limit_ms)
+SendTimeHistory::SendTimeHistory(const Clock* clock,
+                                 int64_t packet_age_limit_ms)
     : clock_(clock), packet_age_limit_ms_(packet_age_limit_ms) {}
 
 SendTimeHistory::~SendTimeHistory() {}