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