MetricSettings getHistogramDefinition(String metricName) {
        if (metricReceiver == null) {
            return null;
        } else {
            return metricReceiver.getMetricDefinition(metricName);
        }
    }
Get histogram definition for an arbitrary metric. Caveat emptor: This
involves reading a volatile.

@param metricName name of the metric to get histogram definition for
@return how to define a new histogram or null
container-core/src/main/java/com/yahoo/metrics/simple/Sample.java