why is this being left without an owner?

Hey Evan - we have a few other folks joining the Instant Tethering effort, and someone else might pick up this issue instead of myself. Don't worry - we haven't forgotten about it!

ok, good to hear. Bugs have a way of getting lost when they're unowned is why I was concerned.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/188faf2ac78aba56b4e8cc65a16b16f1c4118392

commit 188faf2ac78aba56b4e8cc65a16b16f1c4118392
Author: Evan Stade <estade@chromium.org>
Date: Tue Dec 19 00:12:50 2017

Make TetherNotificationPresenter use NotificationDisplayService.

Also make it use NotificationDelegate instead of MessageCenterObserver
(notifiers should keep track of interaction with their notifications
via the former, not the latter).

Also make the unit tests a good deal more streamlined.

Bug:  783018 , 784494 
Change-Id: I9e0d22ced745f650796ff3abc81c9288dce7feec
Reviewed-on: https://chromium-review.googlesource.com/828468
Commit-Queue: Evan Stade <estade@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524874}
[modify] https://crrev.com/188faf2ac78aba56b4e8cc65a16b16f1c4118392/chrome/browser/chromeos/net/tether_notification_presenter.cc
[modify] https://crrev.com/188faf2ac78aba56b4e8cc65a16b16f1c4118392/chrome/browser/chromeos/net/tether_notification_presenter.h
[modify] https://crrev.com/188faf2ac78aba56b4e8cc65a16b16f1c4118392/chrome/browser/chromeos/net/tether_notification_presenter_unittest.cc
[modify] https://crrev.com/188faf2ac78aba56b4e8cc65a16b16f1c4118392/chrome/browser/chromeos/tether/tether_service.cc
[modify] https://crrev.com/188faf2ac78aba56b4e8cc65a16b16f1c4118392/chrome/browser/notifications/stub_notification_display_service.cc