code: func cronTrigger(a cron.StartInvocationAction, now time.Time) *internal.Trigger {
  	return &internal.Trigger{
  		Id:      fmt.Sprintf("cron:v1:%d", a.Generation),
  		Created: google.NewTimestamp(now),
  		Payload: &internal.Trigger_Cron{
  			Cron: &api.CronTrigger{
  				Generation: a.Generation,
  			},
  		},
  	}
  }
docs: // cronTrigger generates a trigger struct from an invocation request generated
  // by the cron state machine.