WakeLock: Add mojo observer API for wake locks

This change tracks system wide wake locks per type and adds a mojo API
to notify clients of wake lock activation and deactivation per type.

BUG=chromium:913353
TEST=WakeLockTest unit tests.

Change-Id: I5a31e5541fce0b88479ffd55362bd8420631c5a1
Reviewed-on: https://chromium-review.googlesource.com/c/1372220
Commit-Queue: Abhishek Bhardwaj <abhishekbh@chromium.org>
Reviewed-by: Elijah Taylor <elijahtaylor@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634926}
12 files changed