arc: support receiving notification of arc stopped from upstart job

Add support for receiving the signal that the ARC++ container has
stopped from an Upstart Job script. After the change on the ChromeOS side
is made to send the stopped signal from the job script instead of from
session_manager, support for receiving the signal from session_manager
will be removed.

Bug: b:133248517
Change-Id: I932778fde1f14a0581c96f0efb4f28892e991b8b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1673862
Commit-Queue: Chris Morin <cmtm@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672225}
5 files changed