GitLab

Extracts code that deals with calling powerd SetBacklightsForcedOff
method from PowerButtonDisplayController to a separate class that can
handle multiple concurrent requests to set backlights off (by keeping
track of the active set backlights forced off requests).

While currently only PowerButtonDisplayController uses
SetBackligthsForcedOff, it's planned to add similar ability to lock
screen note launching code in a follow-up (the idea is to force
backlights off if the lock screen app is launched while the display is
turned off, until the app launch is done).
Goal of BacklightsForcedOffSetter is to prevent these two classes from
conflicting with each other - it will ensure backlights are forced off
as long as at least one backlights forced off request is active.

Backlights can be forced off using
BacklightsForcedOffSetter::ForceBacklightsOff, which returns
ScopedBacklightsForcedOff unique ptr - to stop backlights forced off
request, callers should just reset the returned unique ptr.

BUG=767711
TEST=Press power button, verify display is turned off. Press power
     button again - display is turned on.

Change-Id: Ie47f546edb51659bb82ba4618b069569a2d188c6
Reviewed-on: https://chromium-review.googlesource.com/758963
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Qiang(Joe) Xu <warx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521923}