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Due to internal changes, it makes more sense to have display settings
manager own whether the screen should power off, so reverting the screen
off API to that state and adding a new call for setting whether it
should power off.

BUG=b/156411764
TEST=Build, flash to device, check behaviour

Change-Id: Ib395a96ef7385640ee0bd36e0907f96c73dcd85a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2316666Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Eric Ye <ericye@google.com>
Cr-Commit-Position: refs/heads/master@{#791313}