power: Add wrapper class for wake up alarms API on Chrome OS

This change adds a class that makes the wake up alarm D-Bus API on
Chrome OS easy to use by clients. The D-Bus API was merged in
aec92f8bb5b58c4d654522d8550d53e3e24a8345.

BUG=chromium:913318
TEST=Unit tests and end-to-end alarms via ARC++ applications.

Change-Id: I045af2c6ffbf93b3d44ac09ca217159fcdae18fe
Reviewed-on: https://chromium-review.googlesource.com/c/1372848
Commit-Queue: Abhishek Bhardwaj <abhishekbh@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634959}
5 files changed