GitLab

Ensure that the disconnect handler which calls the caption host is
bound to the same thread. This fixes a data race bug found by
Clusterfuzz.

Bug: 1055150, 1116338
Change-Id: Idfaab83da0b918181bb1296c5e753a06bad388cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359405Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Abigail Klein <abigailbklein@google.com>
Cr-Commit-Position: refs/heads/master@{#799350}