stats/metrickey.go
func DefaultMetricPrefix(name string, tags map[string]string) string {
	return MetricWithPrefix("tchannel.", name, tags)
}
func DefaultMetricPrefix(name string, tags map[string]string) string {
	return MetricWithPrefix("tchannel.", name, tags)
}
// DefaultMetricPrefix is the default mapping for metrics to statsd keys.
// It uses a "tchannel" prefix for all stats.