Fix initializing volume manager in Files app.

Fix initializing volume manager in Files app.

Promise.all was called with a double array [[p1, p2]], instead of [p1, p2],
which caused completing initialization of all volumes before they are added
to the volume list, what caused failing tests in: crrev.com/985533004.

TEST=Fixes test failures in crrev.com/985533004.
BUG=None

Committed: https://crrev.com/147fd75c0ad470da9109dcae72a269e80ecaef4e
Cr-Commit-Position: refs/heads/master@{#321494}

[mtomasz, 2015-03-20 01:31:38]

mtomasz@chromium.org changed reviewers:
+ hirono@chromium.org

[mtomasz, 2015-03-20 01:32:01]

@hirono: PTAL, thanks!

[mtomasz, 2015-03-20 01:32:13]

mtomasz@chromium.org changed reviewers:
+ yawano@chromium.org
- hirono@chromium.org

[mtomasz, 2015-03-20 01:32:22]

@yawano: PTAL. Thanks!

[yawano, 2015-03-20 01:39:12]

lgtm. Thank you!

[mtomasz, 2015-03-20 01:47:31]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2015-03-20 01:48:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1020113002/1

[commit-bot: I haz the power, 2015-03-20 02:02:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-20 02:03:20]

Patchset 1 (id:??) landed as
https://crrev.com/147fd75c0ad470da9109dcae72a269e80ecaef4e
Cr-Commit-Position: refs/heads/master@{#321494}