code: func NewHistogramVec(opts prometheus.HistogramOpts, labelNames []string) *prometheus.HistogramVec {
  	h := prometheus.NewHistogramVec(opts, labelNames)
  	prometheus.MustRegister(h)
  	return h
  }
docs: // NewHistogramVec works like the function of the same name in the prometheus
  // package but it automatically registers the HistogramVec with the
  // prometheus.DefaultRegisterer. If the registration fails, NewHistogramVec
  // panics.