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This adds notifications from ARC about power mode changes and request to
read current state.
Android part: ag/12863924

DD: go/arc_power_control

BUG=b:170982650
TEST=In context of prototype.

Change-Id: I4593eb8284d8473a249d71f00aa5c979bd1c3bdf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2480707Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Yury Khmel <khmel@google.com>
Auto-Submit: Yury Khmel <khmel@google.com>
Cr-Commit-Position: refs/heads/master@{#818814}