Fix ActivateBubble asan failure.

Changing focus of a view may cause UnifiedSystemTrayBubble to destruct.
(See stack trace of https://crbug.com/853434#c6)

At the point UnifiedSystemTrayBubble is deleted, the widget is still
not deleted, so we should explicitly check if the widget is closing.

TEST=manual
BUG=853434

Change-Id: I2d4a146393ad6d0a39d5c8b78ea3c3623d04b91e
Reviewed-on: https://chromium-review.googlesource.com/1107036
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569499}
1 file changed