Re-enable the new SQLitePersistentCookieStore load strategy.

Re-enable the new SQLitePersistentCookieStore load strategy.

When I first turned on the new load strategy, it caused deadlocks during
shutdown. I found and fixed the bug in SequencedWorkerPool.

BUG=448910
Committed: https://crrev.com/043d6b497dda7a39138eca1fb9df89ee340e543b
Cr-Commit-Position: refs/heads/master@{#318305}

[erikchen, 2015-02-26 18:40:44]

erikchen@chromium.org changed reviewers:
+ erikwright@chromium.org

[erikchen, 2015-02-26 18:40:44]

erikwright: Please review.

This CL fixes the deadlock:
https://codereview.chromium.org/956583004/

[erikwright (departed), 2015-02-26 18:45:13]

LGTM.

[erikchen, 2015-02-26 19:40:55]

The CQ bit was checked by erikchen@chromium.org

[commit-bot: I haz the power, 2015-02-26 19:41:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/953993002/1

[commit-bot: I haz the power, 2015-02-26 20:58:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-26 20:59:24]

Patchset 1 (id:??) landed as
https://crrev.com/043d6b497dda7a39138eca1fb9df89ee340e543b
Cr-Commit-Position: refs/heads/master@{#318305}

[erikchen, 2015-03-09 18:35:43]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/992723002/ by erikchen@chromium.org.

The reason for reverting is: This CL causes hangs during shutdown.

https://code.google.com/p/chromium/issues/detail?id=465271.