Fixed flakiness in PolicyTest.FileURLBlacklist.

Re-enabled PolicyTest.FileURLBlacklist.

This test flakes on the Mac. This CL adds additional logging to help diagnose the source of flakiness.

BUG=339240
Committed: https://crrev.com/82405166f151d0d0be73d040aa5b77d309034aa0
Cr-Commit-Position: refs/heads/master@{#295956}

[Joao da Silva, 2014-09-22 11:49:13]

joaodasilva@chromium.org changed reviewers:
+ pneubeck@chromium.org

[Joao da Silva, 2014-09-22 11:49:14]

PTAL

[pneubeck (no reviews), 2014-09-22 12:06:13]

lgtm

seems that this is to get more logging and doesn't fix the problem. Please
mention that in the commit message.

lgtm after you update from EXPECTs to ASSERTs.

[Joao da Silva, 2014-09-22 12:12:22]

All done, thanks for having a look.

[Joao da Silva, 2014-09-22 12:14:03]

The CQ bit was checked by joaodasilva@chromium.org

[commit-bot: I haz the power, 2014-09-22 12:14:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/551323003/80001

[commit-bot: I haz the power, 2014-09-22 12:49:43]

Committed patchset #5 (id:80001) as 32f25a846c060e06d34b6f0fc14a7830eb6b0a36

[commit-bot: I haz the power, 2014-09-22 12:50:22]

Patchset 5 (id:??) landed as
https://crrev.com/82405166f151d0d0be73d040aa5b77d309034aa0
Cr-Commit-Position: refs/heads/master@{#295956}

[jam, 2014-09-28 15:17:37]

A revert of this CL (patchset #5 id:80001) has been created in
https://codereview.chromium.org/608153002/ by jam@chromium.org.

The reason for reverting is: It's causing lots of flakiness on trybots, now that
you added logging look at the past flakiness for more info:

http://chromium-try-flakes.appspot.com/search?q=PolicyTest.FileURLBlacklist.