code: public Histogram histogram(String name, final MetricSupplier<Histogram> supplier) {
          return getOrAdd(name, new MetricBuilder<Histogram>() {
              @Override
              public Histogram newMetric() {
                  return supplier.newMetric();
              }
  
              @Override
              public boolean isInstance(Metric metric) {
                  return Histogram.class.isInstance(metric);
              }
          });
      }
docs: Return the {@link Histogram} registered under this name; or create and register
  a new {@link Histogram} using the provided MetricSupplier if none is registered.
  
  @param name     the name of the metric
  @param supplier a MetricSupplier that can be used to manufacture a histogram
  @return a new or pre-existing {@link Histogram}