Timer is a high-level timer (in contrast to the low-level `Timeout`
class). Timers are started and can be stopped or restarted. When a timer
expires, the provided callback will be triggered.
Timers can be configured to do e.g. exponential backoff when they expire
and how many times they should be automatically restarted.
Bug: webrtc:12614
Change-Id: Id5eddd58dd0af62184b10dd1f98e3e886e3f1d50
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213350
Reviewed-by: Tommi <tommi@webrtc.org>
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33666}
