stats/tally.go
func NewTallyReporter(scope tally.Scope) tchannel.StatsReporter {
	return &wrapper{
		scope:  scope,
		byTags: make(map[knownTags]*taggedScope),
	}
}
func NewTallyReporter(scope tally.Scope) tchannel.StatsReporter {
	return &wrapper{
		scope:  scope,
		byTags: make(map[knownTags]*taggedScope),
	}
}
// NewTallyReporter takes a tally.Scope and wraps it so it ca be used as a
// StatsReporter. The list of metrics emitted is documented on:
// https://tchannel.readthedocs.io/en/latest/metrics/
// The metrics emitted are similar to YARPC, the tags emitted are:
// source, dest, procedure, and retry-count.