The only reason this is required at the moment is to set the
process UID field in the token, that is supposed to make it easier
for controller apps to identify the session. However, if this
visibility is not provided, it shouldn't stop us from creating
the controller for this session.
Also docuement more clearly what UID means in this context.
PiperOrigin-RevId: 490184508
(cherry picked from commit c41a5c84)
