arc: Fix custom notification crash on closing

arc: Fix custom notification crash on closing

Reset surface_ in ArcCustomNotificationView when the underlying
ArcCustomNotificationItem is gone or the notification surface is
removed.

BUG=625220
Committed: https://crrev.com/4f093ef33a9fc0d9661204fc0255b9b0d8dca995
Cr-Commit-Position: refs/heads/master@{#403796}

[xiyuan, 2016-07-01 19:28:10]

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

[yoshiki, 2016-07-05 03:38:11]

lgtm

[xiyuan, 2016-07-05 16:13:16]

The CQ bit was checked by xiyuan@chromium.org

[commit-bot: I haz the power, 2016-07-05 16:13:37]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-07-05 16:50:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-05 16:50:31]

CQ bit was unchecked.

[commit-bot: I haz the power, 2016-07-05 16:52:24]

Description was changed from

==========
arc: Fix custom notification crash on closing

Reset surface_ in ArcCustomNotificationView when the underlying
ArcCustomNotificationItem is gone or the notification surface is
removed.

BUG=625220
==========

to

==========
arc: Fix custom notification crash on closing

Reset surface_ in ArcCustomNotificationView when the underlying
ArcCustomNotificationItem is gone or the notification surface is
removed.

BUG=625220

Committed: https://crrev.com/4f093ef33a9fc0d9661204fc0255b9b0d8dca995
Cr-Commit-Position: refs/heads/master@{#403796}
==========

[commit-bot: I haz the power, 2016-07-05 16:52:26]

Patchset 1 (id:??) landed as
https://crrev.com/4f093ef33a9fc0d9661204fc0255b9b0d8dca995
Cr-Commit-Position: refs/heads/master@{#403796}