Code review comment for lp:~nick-dedekind/mir/trusted_sessions

In TrustSession::add_trusted_child() there's a call "session->begin_trust_session();" which will send a mir_event_type_trust_session_state_change to the "child" process.

But AIUI the child isn't the "helper" process that created the trust session and can't have registered a mir_trust_session_event_callback (which needs a trust session).