Convert auto_screen_brightness::Adapter to use Mojo power manager client

PowerManagerMojoClient/Controller implement PowerManagerBecameAvailable
and SetScreenBrightness.

Bug: 644348
Change-Id: I997942403a9ba06c9bbb866007ff0e408b604e1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583059
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654073}
10 files changed