code: func (es *EventSystem) SubscribeNewHeads(headers chan *types.Header) *Subscription {
  	sub := &subscription{
  		id:        rpc.NewID(),
  		typ:       BlocksSubscription,
  		created:   time.Now(),
  		logs:      make(chan []*types.Log),
  		hashes:    make(chan []common.Hash),
  		headers:   headers,
  		installed: make(chan struct{}),
  		err:       make(chan error),
  	}
  	return es.subscribe(sub)
  }
docs: // SubscribeNewHeads creates a subscription that writes the header of a block that is
  // imported in the chain.