To be able to reuse VideoBroadcaster, that class needs to be
officially threadsafe. It already had the needed locks, but thread
checkers have to be deleted to allow calls to AddOrUpdateSink on
multiple threads (worker thread + encoder thread).
Bug: webrtc:6353, webrtc:10147
Change-Id: I16128ac205c566f09402b6f22587a340d9a983c1
Reviewed-on: https://webrtc-review.googlesource.com/c/115201
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26073}
3793bb447a