Emit ash-initialized upstart signal on ash shell init

Adds EmitAshInitialized method to session_manager_client - the
method requests from session manager to emit "ash-initialized"
upstart signal. The signal can be used to run upstart jobs that
should be run when ash is initialized - for example, to run hammerd
task, which will ensure that detachable base pairing signals are
emitted after ash starts observing dbus signals emitted by hammerd.
DetachableBaseHandler relies on hammerd signals to determine when,
whether a detachable base notification should be shown to the user, so
these signals should be re-emitted whenever ash is (re)started.

Makes ash::Shell::Init call the new session manager method to actually
emit the upstart signal once it's done initializing.

BUG=818057

Change-Id: If901e125f8f3f8563c22a0633644a0c6ff143f7d
Reviewed-on: https://chromium-review.googlesource.com/981330
Commit-Queue: Toni Barzic <[email protected]>
Reviewed-by: Dan Erat <[email protected]>
Reviewed-by: James Cook <[email protected]>
Cr-Commit-Position: refs/heads/master@{#547082}
5 files changed