Introduces SequenceChecker, merging the functionality of ThreadChecker
and SequencedTaskChecker. Also making the two latter use the former as
the underlying implementation for backwards compatibility.
This allows code that uses thread checker to accept running on a thread
pool backed task queue.
Bug: webrtc:10365
Change-Id: Ifefc4925694f263088a8a095fdf98a2407c62081
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/129721
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@{#27365}