As chatted with Oshima-san, he kindly helps to fix this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/870290f623b47e436d231e354c84b8723bb7000a

commit 870290f623b47e436d231e354c84b8723bb7000a
Author: edcourtney <edcourtney@chromium.org>
Date: Fri May 19 05:15:08 2017

[Notifications] Fix swipe to close for ARC notifications.

Change ArcCustomNotificationView::EventForwarder to not directly invoke On*Event methods of ArcCustomNotificationView (which then call up to the parent). Instead, re-dispatch them to the containing widget, which should handle the event propagation, letting SlideOutController get events as it should. A consequence of this is that I had to add a delegate method to SlideOutController to update ArcCustomNotificationView::SlideHelper. This is because ArcCustomNotificationView will no longer get the gesture events, since it is no longer being called directly from EventForwarder.

BUG= 719407 

Review-Url: https://codereview.chromium.org/2873553002
Cr-Commit-Position: refs/heads/master@{#473094}

[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/arc/notification/arc_custom_notification_view.cc
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/arc/notification/arc_custom_notification_view.h
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/custom_notification_content_view_delegate.h
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/custom_notification_view.cc
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/custom_notification_view.h
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/custom_notification_view_unittest.cc
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/message_view.cc
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/message_view.h
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/slide_out_controller.cc
[modify] https://crrev.com/870290f623b47e436d231e354c84b8723bb7000a/ui/message_center/views/slide_out_controller.h

Requesting merge to M59. Thanks~!

I believe all the preliminary patches that needed merging first have now made it over to M59 (3071).

Your change meets the bar and is auto-approved for M59. Please go ahead and merge the CL to branch 3071 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), gkihumba@(ChromeOS), Abdul Syed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Please go ahead and merge this to M59, thanks.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e33f895d0e3263a25c8e7cd114bfb793ea99fe83

commit e33f895d0e3263a25c8e7cd114bfb793ea99fe83
Author: yoshiki iguchi <yoshiki@chromium.org>
Date: Mon May 22 05:52:20 2017

[Notifications] Fix swipe to close for ARC notifications.

Change ArcCustomNotificationView::EventForwarder to not directly invoke On*Event methods of ArcCustomNotificationView (which then call up to the parent). Instead, re-dispatch them to the containing widget, which should handle the event propagation, letting SlideOutController get events as it should. A consequence of this is that I had to add a delegate method to SlideOutController to update ArcCustomNotificationView::SlideHelper. This is because ArcCustomNotificationView will no longer get the gesture events, since it is no longer being called directly from EventForwarder.

BUG= 719407 

Review-Url: https://codereview.chromium.org/2873553002
Cr-Commit-Position: refs/heads/master@{#473094}
(cherry picked from commit 870290f623b47e436d231e354c84b8723bb7000a)

Review-Url: https://codereview.chromium.org/2897903002 .
Cr-Commit-Position: refs/branch-heads/3071@{#647}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/arc/notification/arc_custom_notification_view.cc
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/arc/notification/arc_custom_notification_view.h
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/custom_notification_content_view_delegate.h
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/custom_notification_view.cc
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/custom_notification_view.h
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/custom_notification_view_unittest.cc
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/message_view.cc
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/message_view.h
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/slide_out_controller.cc
[modify] https://crrev.com/e33f895d0e3263a25c8e7cd114bfb793ea99fe83/ui/message_center/views/slide_out_controller.h

Thanks for merging that for me Yoshiki-san.

9460.50.0, 59.0.3071.71