One more case to verify that clicking on closing button should not crash. (b/30768240).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/416f1f674c873e3b58963e64a2ef01e52dcfbe5e

commit 416f1f674c873e3b58963e64a2ef01e52dcfbe5e
Author: xiyuan <xiyuan@chromium.org>
Date: Thu Aug 11 05:21:12 2016

arc: Custom notification improvements

- Install a pre target event handler to notification surface window
  to forward events to hosting ArcCustomNotificationView;
- Only show close button when mouse hovering;
- Add SlideHelper to observe slide transform/animation and swap between
  a notification surface copy and real surface when a slide starts/stops;

BUG= 635566 ,636625
TEST=Manual. Close button only shows up when mouse hovering. Backspace/delete
  key dismisses the custom notification. Swipe gesture works as regular
  Chrome notification. Closing via close button in message list does not crash.

Review-Url: https://codereview.chromium.org/2221073002
Cr-Commit-Position: refs/heads/master@{#411272}

[modify] https://crrev.com/416f1f674c873e3b58963e64a2ef01e52dcfbe5e/ui/arc/BUILD.gn
[modify] https://crrev.com/416f1f674c873e3b58963e64a2ef01e52dcfbe5e/ui/arc/arc.gyp
[modify] https://crrev.com/416f1f674c873e3b58963e64a2ef01e52dcfbe5e/ui/arc/notification/DEPS
[modify] https://crrev.com/416f1f674c873e3b58963e64a2ef01e52dcfbe5e/ui/arc/notification/arc_custom_notification_view.cc
[modify] https://crrev.com/416f1f674c873e3b58963e64a2ef01e52dcfbe5e/ui/arc/notification/arc_custom_notification_view.h

Merge to M53 is requested on issue 636625.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/04d983055adc49b17a9e6a4c08b03104c1453098

commit 04d983055adc49b17a9e6a4c08b03104c1453098
Author: Xiyuan Xia <xiyuan@google.com>
Date: Mon Aug 15 17:42:29 2016

Merge "arc: Custom notification improvements"

> - Install a pre target event handler to notification surface window
>   to forward events to hosting ArcCustomNotificationView;
> - Only show close button when mouse hovering;
> - Add SlideHelper to observe slide transform/animation and swap between
>   a notification surface copy and real surface when a slide starts/stops;
>
> BUG= 635566 ,636625
> TEST=Manual. Close button only shows up when mouse hovering. Backspace/delete
>   key dismisses the custom notification. Swipe gesture works as regular
>   Chrome notification. Closing via close button in message list does not crash.
>
> Review-Url: https://codereview.chromium.org/2221073002
> Cr-Commit-Position: refs/heads/master@{#411272}
> (cherry picked from commit 416f1f674c873e3b58963e64a2ef01e52dcfbe5e)

Review URL: https://codereview.chromium.org/2244333002 .

Cr-Commit-Position: refs/branch-heads/2785@{#592}
Cr-Branched-From: 68623971be0cfc492a2cb0427d7f478e7b214c24-refs/heads/master@{#403382}

[modify] https://crrev.com/04d983055adc49b17a9e6a4c08b03104c1453098/ui/arc/BUILD.gn
[modify] https://crrev.com/04d983055adc49b17a9e6a4c08b03104c1453098/ui/arc/arc.gyp
[modify] https://crrev.com/04d983055adc49b17a9e6a4c08b03104c1453098/ui/arc/notification/DEPS
[modify] https://crrev.com/04d983055adc49b17a9e6a4c08b03104c1453098/ui/arc/notification/arc_custom_notification_view.cc
[modify] https://crrev.com/04d983055adc49b17a9e6a4c08b03104c1453098/ui/arc/notification/arc_custom_notification_view.h

ChromeOS build 8530.96.0 / 53.0.2785.154