The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a27abd29f967f530c620acd7ab302066ee205382

commit a27abd29f967f530c620acd7ab302066ee205382
Author: Robert Liao <robliao@chromium.org>
Date: Wed Jan 24 18:46:48 2018

Change Autofill Helper TaskScheduler::FlushForTesting() to Wait on TaskRunner tasks

base::TaskScheduler::GetInstance()->FlushForTesting() may have been too
big of a hammer to use here. I've moved this code back to a previous
style of waiting for the DB task runner to flush
(http://crrev.com/490312).

The main issue here is that FlushForTesting() often gets called on the
main thread, and with MessageLoop Task Scheduler redirection,
FlushForTesting will wait for MessageLoop tasks to complete. If a
MessageLoop task is waiting for the main thread to process a task and
the main thread is calling FlushForTesting(), a deadlock will occur.

If these components start using other task runners, a completion
callback mechanism will best support this file going forward.

BUG= 667892 ,749310

Change-Id: I0693bf7a00b25be9a95e2bae89ec3b4167ba4d4a
Reviewed-on: https://chromium-review.googlesource.com/874817
Reviewed-by: Pavel Yatsuk <pavely@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531624}
[modify] https://crrev.com/a27abd29f967f530c620acd7ab302066ee205382/chrome/browser/sync/test/integration/autofill_helper.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a0a5c4046775f09dfff103972baf6ab12e33acc5

commit a0a5c4046775f09dfff103972baf6ab12e33acc5
Author: Robert Liao <robliao@chromium.org>
Date: Wed Mar 14 23:02:43 2018

Add TaskScheduler Support to the MessageLoop Unit Tests

With TaskScheduler redirection, the MessageLoop will redirect tasks
only if a TaskScheduler is present. Otherwise, it will handle task
dispatch itself similar to today.

Direct dispatch is only expected to happen in unit tests and some
integration tests.

BUG=749310

Change-Id: Ia35f17a7a15155c8893020e7174573144bf7afb7
Reviewed-on: https://chromium-review.googlesource.com/932827
Commit-Queue: Robert Liao <robliao@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543232}
[modify] https://crrev.com/a0a5c4046775f09dfff103972baf6ab12e33acc5/base/message_loop/message_loop_unittest.cc

Currently marking all unowned TaskScheduler features as P3 (not time critical), will re-triage when cycles free up.