Execute error callbacks on the right thread.

This is a long standing issue exposed by more frequent error
callbacks being thrown.

Fixed: 329169301
Change-Id: I4451e9d685fd10b85c36074c280e7cef568501c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5368314


Commit-Queue: Evan Liu <evliu@google.com>
Reviewed-by: Evan Liu <evliu@google.com>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1271855}