GitLab

SingleThreadTaskRunner is still required, but we should not need a
specific BrowserThread.

This is part of the task scheduler migration effort.

BUG=None

Change-Id: I23dfba4f9acd51176d8df18f6269090494808a69
Reviewed-on: https://chromium-review.googlesource.com/594719Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491432}