Add a unittest that DeleteAll(CookieMonster*) does flush

Add a unittest that DeleteAll(CookieMonster*) does flush

The unittest ensure that DeleteAll(CookieMonster*) does flush and that the
flush_count is valid after DeleteAll() calls.

BUG=None

Committed: https://crrev.com/444025d2c345aa933460f6e5814fe2b205f2225b
Cr-Commit-Position: refs/heads/master@{#325437}

[sdefresne, 2015-04-14 08:52:51]

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

[sdefresne, 2015-04-14 08:52:51]

erikwright: this is a test that we have downstream (iOS only) and that I think
should be run upstream too (or deleted downstream). I did not originally write
this test.

Could you please take a look?

[erikwright (departed), 2015-04-16 13:13:12]

LGTM.

[sdefresne, 2015-04-16 13:28:52]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-04-16 13:29:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1083883002/1

[commit-bot: I haz the power, 2015-04-16 13:59:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-16 14:00:23]

Patchset 1 (id:??) landed as
https://crrev.com/444025d2c345aa933460f6e5814fe2b205f2225b
Cr-Commit-Position: refs/heads/master@{#325437}