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

webrtc/modules/congestion_controller/probe_controller.h

Index: webrtc/modules/congestion_controller/probe_controller.h
diff --git a/webrtc/modules/congestion_controller/probe_controller.h b/webrtc/modules/congestion_controller/probe_controller.h
index ccce7d3ec6c1d75147529f9181bf1dc04a48f404..28cd10225fe50f9d88b96aca3cfa610348e82ed4 100644
--- a/webrtc/modules/congestion_controller/probe_controller.h
+++ b/webrtc/modules/congestion_controller/probe_controller.h
@@ -26,7 +26,7 @@ class Clock;
 // bitrate is adjusted by an application.
 class ProbeController {
  public:
-  ProbeController(PacedSender* pacer, Clock* clock);
+  ProbeController(PacedSender* pacer, const Clock* clock);
 
   void SetBitrates(int64_t min_bitrate_bps,
                    int64_t start_bitrate_bps,
@@ -61,7 +61,7 @@ class ProbeController {
 
   rtc::CriticalSection critsect_;
   PacedSender* const pacer_;
-  Clock* const clock_;
+  const Clock* const clock_;
   NetworkState network_state_ GUARDED_BY(critsect_);
   State state_ GUARDED_BY(critsect_);
   int64_t min_bitrate_to_probe_further_bps_ GUARDED_BY(critsect_);