func (mg *MetricsGroup) LockAndSetBuckets(buckets []string) func() {
	mg.bucketsLock.Lock()
	mg.buckets = buckets
	return func() {
		mg.bucketsLock.Unlock()
	}
}

// MetricFQN - returns the fully qualified name for the given metric name.
func (mg *MetricsGroup) MetricFQN(name MetricName) string {
	v, ok := mg.descriptorMap[name]
	if !ok {
		// This should never happen.
		return ""
	}