[Download Notification] Disable download notification by default on ChromeOS

[Download Notification] Disable download notification by default on ChromeOS

This patch disables download notification by default on ChromeOS. User still can enable it on chrome://flag explicitly.

On the other platform, it has already been disabled by default.

BUG=523161
TEST=none
TBR=asanka@chromium.org
R=fukino@chromium.org

Committed: https://crrev.com/175c6d056fdf13de95531b780659ef0692260e1d
Cr-Commit-Position: refs/heads/master@{#344727}

[yoshiki, 2015-08-21 06:37:22]

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

[yoshiki, 2015-08-21 06:37:36]

Fukino-san, could you take a look? Thanks.

[fukino, 2015-08-21 07:57:44]

lgtm!

[yoshiki, 2015-08-21 07:58:23]

Thanks!

[yoshiki, 2015-08-21 07:58:27]

The CQ bit was checked by yoshiki@chromium.org

[commit-bot: I haz the power, 2015-08-21 07:58:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1303193002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1303193002/1

[commit-bot: I haz the power, 2015-08-21 09:23:25]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-21 09:24:01]

Patchset 1 (id:??) landed as
https://crrev.com/175c6d056fdf13de95531b780659ef0692260e1d
Cr-Commit-Position: refs/heads/master@{#344727}