Files.app: Skip updating subdirectories of a volume whose display root is not gotten yet.

Files.app: Skip updating subdirectories of a volume whose display root is not gotten yet.

Now that volumes other than Google Drive can be expanded in the directory tree,
there is a case that subdirectories are queried befor the displayroot of volume is
obtained. In this case, we should skip updating subdirectories. After the displayroot
is obtained, updateSubDirectories will be called.

BUG=459534
TEST=manually check the steps described in the issue.

Committed: https://crrev.com/94b2fd417e4fee909fe42b6e801e0fc3b2098039
Cr-Commit-Position: refs/heads/master@{#316994}

[fukino, 2015-02-18 11:48:27]

fukino@chromium.org changed reviewers:
+ yawano@chromium.org

[fukino, 2015-02-18 11:48:27]

PTAL. Thanks!

[yawano, 2015-02-19 01:33:49]

lgtm. Thank you!

[fukino, 2015-02-19 05:25:49]

The CQ bit was checked by fukino@chromium.org

[commit-bot: I haz the power, 2015-02-19 05:26:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/940443003/1

[commit-bot: I haz the power, 2015-02-19 05:53:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-19 05:53:48]

Patchset 1 (id:??) landed as
https://crrev.com/94b2fd417e4fee909fe42b6e801e0fc3b2098039
Cr-Commit-Position: refs/heads/master@{#316994}