GitLab

Creates a TimeLimitNotifier class to handle notification details for
bedtime and screen time limits, and adds tests.

Later, this can be used to hide the notification when it no longer
applies, probably by listening to some event.

Bug: 898000
Change-Id: Ie7844d6d0639815eac967062ae83b308346485d8
Reviewed-on: https://chromium-review.googlesource.com/c/1295182
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Aga Wronska <agawronska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603740}