Removes all const Clock*.

This prepares for making the Clock interface fully mutable.

Calls to the time functions in Clock can have side effects in some
circumstances. It's also questionable if it's a good idea to allow
repeated calls to a const method return different values without
any changed to the class instance.

Bug: webrtc:9883
Change-Id: I96fb9230705f7c80a4c0702132fd9dc73899fc5e
Reviewed-on: https://webrtc-review.googlesource.com/c/120347
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26467}
diff --git a/call/rtp_transport_controller_send.h b/call/rtp_transport_controller_send.h
index deef040..c1b576e 100644
--- a/call/rtp_transport_controller_send.h
+++ b/call/rtp_transport_controller_send.h
@@ -133,7 +133,7 @@
   void PostUpdates(NetworkControlUpdate update) RTC_RUN_ON(task_queue_);
   void UpdateControlState() RTC_RUN_ON(task_queue_);
 
-  const Clock* const clock_;
+  Clock* const clock_;
   PacketRouter packet_router_;
   std::vector<std::unique_ptr<RtpVideoSenderInterface>> video_rtp_senders_;
   PacedSender pacer_;