GitLab

- ui/message_center/mojo/ => ui/message_center/public/mojo/
- ui/message_center/notification.cc, etc. =>
      ui/message_center/public/cpp

The public directory contains code that will be compiled into both
Chrome and Ash binaries. On CrOS, the non-public directory will only
be compiled in Ash. On Linux and Windows, the non-public directory
will still be compiled into the browser.

This CL doesn't actually enact any of the above, but it sets up
separate build targets and begins to get dependencies correct. For
example, Notification is now blocked from depending on MessageCenter.

Bug: 578868
Change-Id: Ie32e0f4ab114ec292462a7b87c94b1dcee0540da
Reviewed-on: https://chromium-review.googlesource.com/887978
Commit-Queue: Evan Stade <estade@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532278}