Reland "Re-enable the new SQLitePersistentCookieStore load strategy."

Reland "Re-enable the new SQLitePersistentCookieStore load strategy."

Reason for revert:
The source of the crash was another bug in SequencedWorkerPool. I just landed a fix for that:
https://codereview.chromium.org/994483005/

So I'm going to reland this CL.

Original issue's description:
> Revert of Re-enable the new SQLitePersistentCookieStore load strategy. (patchset #1 id:1 of https://codereview.chromium.org/953993002/)
>
> Reason for revert:
> This CL causes hangs during shutdown.
>
> https://code.google.com/p/chromium/issues/detail?id=465271
>
> Original issue's description:
> > 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}
>
> TBR=erikwright@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=448910
>
> Committed: https://crrev.com/24ab88b28d3fcdb67a919527e67c49ba5d55ed93
> Cr-Commit-Position: refs/heads/master@{#319696}

TBR=erikwright@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=448910
Committed: https://crrev.com/ecd42cf5ae19e2807067ad1add9430af0d34510d
Cr-Commit-Position: refs/heads/master@{#320605}

[erikchen, 2015-03-13 23:47:26]

Created Revert of Revert of Re-enable the new SQLitePersistentCookieStore load
strategy.

[erikchen, 2015-03-13 23:47:33]

The CQ bit was unchecked by erikchen@chromium.org

[erikchen, 2015-03-13 23:48:24]

The CQ bit was checked by erikchen@chromium.org

[commit-bot: I haz the power, 2015-03-13 23:48:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1005953003/1

[commit-bot: I haz the power, 2015-03-13 23:49:51]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-13 23:50:21]

Patchset 1 (id:??) landed as
https://crrev.com/ecd42cf5ae19e2807067ad1add9430af0d34510d
Cr-Commit-Position: refs/heads/master@{#320605}