Here's the screenshot. As shown there were 4 notifications from Docs and 1 from Sheets. I think these came from web apps rather than Android apps.

Deleted: non-discardable.png 47.6 KB

	non-discardable.png 47.6 KB View Download

I confirmed it on ToT. The status of the button is wrong just after the message center opens. It happens only when there ares only ARC notifications.

Eliot, could you investigate?

The statuses of buttons are updated in MessageCenterView::UpdateButtonBarStatus(). I think (1) this method is not called correctly when the message center opens, or (2) all notifications are treated as pinned (= non-closable) wrongly when the message center opens.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/581285b278ce65ddf216a03295333bd396239c03

commit 581285b278ce65ddf216a03295333bd396239c03
Author: edcourtney <edcourtney@chromium.org>
Date: Thu Feb 02 05:07:24 2017

[arc notifications] Inspect pinned flag directly for IsPinned().

When an ARC notification comes, the 'discard notifications' button in
the notifications tray is greyed out until you hover over the
notification. ArcCustomNotificationView::ContentViewDelegate would
check whether ArcCustomNotificationView::floating_close_button_ existed
to determine if the notification is pinned or not. Pinned notifications
cannot be closed. The floating close button is created if the notification
is not pinned. However, it is created after the check inside
ContentViewDelegate. Instead, inspect the pinned state directly from
ArcCustomNotificationItem.

BUG= 685467 

Review-Url: https://codereview.chromium.org/2670493002
Cr-Commit-Position: refs/heads/master@{#447698}

[modify] https://crrev.com/581285b278ce65ddf216a03295333bd396239c03/ui/arc/notification/arc_custom_notification_view.cc