code: public void registerUpdater(Scheduler scheduler,
        SessionNotifier sessionNotifier) {
      this.scheduler = scheduler;
      this.sessionNotifier = sessionNotifier;
      context.registerUpdater(this);
    }
docs: Set the scheduler and start the updating.  The metrics won't be reported
  until this is called.
  
  @param scheduler Scheduler for this cluster manager.
  @param sessionNotifier Session Notifier for this cluster manager.