Ability to emulate degraded networks using DegradedCall has not
been covered by tests and it is crashing due to DCHECKs.
Fix threading issues so this no longer crash.
Bug: None
Change-Id: I9276dfb1f71762faa02146af0bfaab713bebb7f7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/276060
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Daniel.L (Byoungchan) Lee <daniel.l@hpcnt.com>
Cr-Commit-Position: refs/heads/main@{#38216}