[BackgroundSync] Clean up some tests

[BackgroundSync] Clean up some tests

Cleaning up some tests to use helper functions and remove dangling
pointers. It also fixes the DisabledManagerWorksAfterBrowserRestart
test which wasn't initializing after creating a new manager.

Committed: https://crrev.com/6988e2530e4f016e718055040a0bee9cdfe6c0f8
Cr-Commit-Position: refs/heads/master@{#333074}

[jkarlin, 2015-06-05 16:43:33]

jkarlin@chromium.org changed reviewers:
+ jsbell@chromium.org

[jkarlin, 2015-06-05 16:43:35]

Hi Josh, can you please review this quick cleanup cl? Thanks!

[jsbell, 2015-06-05 16:51:21]

lgtm

[jkarlin, 2015-06-05 16:53:14]

The CQ bit was checked by jkarlin@chromium.org

[commit-bot: I haz the power, 2015-06-05 16:53:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1148853005/1

[commit-bot: I haz the power, 2015-06-05 17:01:28]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-05 17:02:26]

Patchset 1 (id:??) landed as
https://crrev.com/6988e2530e4f016e718055040a0bee9cdfe6c0f8
Cr-Commit-Position: refs/heads/master@{#333074}