Add helper methods to ServiceWorkerJobTest

Add helper methods to ServiceWorkerJobTest

To reduce the amount of repetition, this patch adds some helper methods
to ServiceWorkerJobTest that run an asynchronous task and verifie the
result.

TEST=content_unittests --gtest_filter='ServiceWorkerJobTest.*'
BUG=

Committed: https://crrev.com/bc3def1a9c250292c314835387a9bfbbf372b6f3
Cr-Commit-Position: refs/heads/master@{#314234}

[Kunihiko Sakamoto, 2015-02-02 11:01:31]

ksakamoto@chromium.org changed reviewers:
+ falken@chromium.org

[Kunihiko Sakamoto, 2015-02-02 11:01:32]

PTAL if you have time. Thanks!

https://codereview.chromium.org/893983002/diff/1/content/browser/service_work...
File content/browser/service_worker/service_worker_job_unittest.cc (left):

https://codereview.chromium.org/893983002/diff/1/content/browser/service_work...
content/browser/service_worker/service_worker_job_unittest.cc:336:
SERVICE_WORKER_OK, &called, &new_registration));
I think there was a bug here; |new_registration| should be
|new_registration_by_pattern|.

[falken, 2015-02-02 11:41:25]

lgtm, the tests are a lot a nicer now.

[Kunihiko Sakamoto, 2015-02-03 01:24:57]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2015-02-03 01:25:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/893983002/1

[commit-bot: I haz the power, 2015-02-03 01:30:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-03 01:32:18]

Patchset 1 (id:??) landed as
https://crrev.com/bc3def1a9c250292c314835387a9bfbbf372b6f3
Cr-Commit-Position: refs/heads/master@{#314234}