Add test storage monitor for MediaGalleries Private API browser test.

Add test storage monitor for this browser test.

It looks like the test was flaky because this test slipped through the cracks.
We weren't initializing the storage monitor, so there was a race where it
might not be fully initialized when the test ran. Switched to using the test
storage monitor as the other API browser tests do (and are not flaky).

R=vandebo@chromium.org
BUG=247336
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=207866

[vandebo (ex-Chrome), 2013-06-20 21:48:37]

LGTM

[commit-bot: I haz the power, 2013-06-20 22:07:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/gbillock@chromium.org/17504004/1

[commit-bot: I haz the power, 2013-06-20 22:40:34]

Retried try job too often on chromium_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=chromium_p...

[commit-bot: I haz the power, 2013-06-20 22:41:49]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/gbillock@chromium.org/17504004/1

[vandebo (ex-Chrome), 2013-06-20 22:42:36]

+asargent for OWNERS review.

[asargent_no_longer_on_chrome, 2013-06-20 23:39:33]

lgtm

[commit-bot: I haz the power, 2013-06-21 14:38:19]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/gbillock@chromium.org/17504004/1

[commit-bot: I haz the power, 2013-06-21 17:00:38]

Change committed as 207866