GitLab

Previously all Assistant notifications were Message Center
notifications. Now, we'll support notifications of type:

- kInAssistant
- kPreferInAssistant
- kSystem

The |kInAssistant| and |kPreferInAssistant| types are currently only
used to support timer notification UX requirements.

Still TODO: Entry/exit animations for in-Assistant notifications.

Bug: b:118654460
Change-Id: I815789d89008ff55318d7b6e8c9492b07849f2ca
Reviewed-on: https://chromium-review.googlesource.com/c/1480549Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: David Black <dmblack@google.com>
Cr-Commit-Position: refs/heads/master@{#634921}