Fix race condition in ExtensionApiTest.Messaging.

Fix race condition in ExtensionApiTest.Messaging.

chrome.tabs.onUpdated may fire when the listener is not set up yet.

BUG=

Committed: https://crrev.com/0d9c77423b7733dfa7f3cf4545a2884a1379400b
Cr-Commit-Position: refs/heads/master@{#293637}

[Alexander Semashko, 2014-09-04 11:44:36]

ahest@yandex-team.ru changed reviewers:
+ samuong@chromium.org

[samuong, 2014-09-05 17:12:34]

samuong@chromium.org changed reviewers:
+ mpcomplete@chromium.org
- samuong@chromium.org

[samuong, 2014-09-05 17:12:53]

This looks reasonable to me but I'm probably not the best person to do the
review.

+mpcomplete@ since he's one of the owners of the messaging api - Matt, do you
mind doing a review of this?

[Matt Perry, 2014-09-05 22:28:04]

lgtm

[Alexander Semashko, 2014-09-06 08:21:51]

The CQ bit was checked by ahest@yandex-team.ru

[commit-bot: I haz the power, 2014-09-06 08:23:46]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ahest@yandex-team.ru/537953002/1

[commit-bot: I haz the power, 2014-09-06 13:42:40]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-06 13:42:41]

Exceeded time limit waiting for builds to trigger.

[Alexander Semashko, 2014-09-06 14:20:00]

The CQ bit was checked by ahest@yandex-team.ru

[commit-bot: I haz the power, 2014-09-06 14:20:59]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ahest@yandex-team.ru/537953002/1

[commit-bot: I haz the power, 2014-09-06 16:21:47]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-06 16:21:48]

Exceeded time limit waiting for builds to trigger.

[Alexander Semashko, 2014-09-06 21:10:03]

The CQ bit was checked by ahest@yandex-team.ru

[commit-bot: I haz the power, 2014-09-06 21:11:10]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ahest@yandex-team.ru/537953002/1

[commit-bot: I haz the power, 2014-09-06 21:17:12]

Committed patchset #1 (id:1) as 05f9a7aee8065d9808389d7a4ea53cf9cce1cbff

[commit-bot: I haz the power, 2014-09-10 03:43:25]

Patchset 1 (id:??) landed as
https://crrev.com/0d9c77423b7733dfa7f3cf4545a2884a1379400b
Cr-Commit-Position: refs/heads/master@{#293637}