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

webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h

Index: webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h b/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
index c6931515e1ae9212c8941e74d2a11298ce467fb2..83ae07844536810a078af53ea66bdd507fd5881d 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
+++ b/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
@@ -32,7 +32,7 @@ class TransportFeedback;
 
 class RemoteEstimatorProxy : public RemoteBitrateEstimator {
  public:
-  RemoteEstimatorProxy(Clock* clock, PacketRouter* packet_router);
+  RemoteEstimatorProxy(const Clock* clock, PacketRouter* packet_router);
   virtual ~RemoteEstimatorProxy();
 
   void IncomingPacket(int64_t arrival_time_ms,
@@ -57,7 +57,7 @@ class RemoteEstimatorProxy : public RemoteBitrateEstimator {
       EXCLUSIVE_LOCKS_REQUIRED(&lock_);
   bool BuildFeedbackPacket(rtcp::TransportFeedback* feedback_packet);
 
-  Clock* const clock_;
+  const Clock* const clock_;
   PacketRouter* const packet_router_;
   int64_t last_process_time_ms_;