Use RunLoop, but do not call RunUntilIdle() multiple times

Use RunLoop, but do not call RunUntilIdle() multiple times

In unit tests for MidiManager, RunLoop was used, and is used to wait
a posted task finished. But, RunUntilIdle() can not be called
multiple times. To avoid this restriction, we can just create new
instance again for another iteration.

TEST=media_unittests

Committed: https://crrev.com/a42e46ee2110aeebb70d9787a0aa05997ec9c67a
Cr-Commit-Position: refs/heads/master@{#300240}

[Takashi Toyoshima, 2014-10-18 15:27:44]

toyoshim@chromium.org changed reviewers:
+ yhirano@chromium.org

[Takashi Toyoshima, 2014-10-18 15:29:47]

RunLoop.RunUntilIdle() is called multiple times in another test, and this is
potential issue. I didn't notice at the last time, but creating new RunLoop
instance is easier solution.

[yhirano, 2014-10-20 02:29:49]

lgtm

[Takashi Toyoshima, 2014-10-20 02:34:02]

The CQ bit was checked by toyoshim@chromium.org

[commit-bot: I haz the power, 2014-10-20 02:34:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/656793004/1

[commit-bot: I haz the power, 2014-10-20 09:37:18]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-20 09:38:22]

Patchset 1 (id:??) landed as
https://crrev.com/a42e46ee2110aeebb70d9787a0aa05997ec9c67a
Cr-Commit-Position: refs/heads/master@{#300240}