GitLab

Register cras_audio_handler to be an observer of MediaController in
order to receive update of media session playback status. Parse such
playback status into string and call corresponding AudioClient function
to propagate the information further to DBUS.

BUG=b:147367681
TEST=chromeos_unittests

Change-Id: I122fa0d3aa5f59a5828c0075617271fcf61ede94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076061Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Jenny Zhang <jennyz@chromium.org>
Commit-Queue: Michael Sun <michaelfsun@google.com>
Cr-Commit-Position: refs/heads/master@{#746176}