@classmethod
def activate(cls, flow_task, prev_activation, token):
    """Instantiate new task."""
    task = flow_task.flow_class.task_class(process=prev_activation.process,
        flow_task=flow_task, token=token)
    task.save()
    task.previous.add(prev_activation.task)
    activation = cls()
    activation.initialize(flow_task, task)
    activation.perform()
    return activation
