Dispatch directory-changed event before rescan starts.

Dispatch directory-changed event before rescan starts.

Directory rescan sometimes uses up IO and blocks other IOs which are necessary
for updating the top-left breadcrumb. While this CL does not solve the real
cause of the issue, this CL mitigates the problem by dispatching event earlier.

BUG=459864
TEST=manually tested as described in the issue

Committed: https://crrev.com/3027da7aee006ad04e084690d6ea410a31969728
Cr-Commit-Position: refs/heads/master@{#317021}

[yawano, 2015-02-19 10:03:47]

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

[yawano, 2015-02-19 10:03:48]

PTAL. Thank you!

[fukino, 2015-02-19 10:09:00]

On 2015/02/19 10:03:48, yawano wrote:
> PTAL. Thank you!

lgtm.

[yawano, 2015-02-19 10:09:34]

On 2015/02/19 10:09:00, fukino wrote:
> On 2015/02/19 10:03:48, yawano wrote:
> > PTAL. Thank you!
> 
> lgtm.

Thank you!

[yawano, 2015-02-19 10:09:42]

The CQ bit was checked by yawano@chromium.org

[commit-bot: I haz the power, 2015-02-19 10:10:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/943473002/1

[commit-bot: I haz the power, 2015-02-19 10:31:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-19 10:32:21]

Patchset 1 (id:??) landed as
https://crrev.com/3027da7aee006ad04e084690d6ea410a31969728
Cr-Commit-Position: refs/heads/master@{#317021}

[yawano, 2015-02-20 07:27:35]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/937423002/ by yawano@chromium.org.

The reason for reverting is: This CL broke as described in
http://crbug.com/460398.
This issue is going to be fixed in different way with another CL..