Added unit annotation supports onto tsmon in go.

common/tsmon/types/metric.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package types
 
 import (
         "time"
 
         "github.com/luci/luci-go/common/tsmon/distribution"
 )
 
 // Metric is the low-level interface provided by all metrics.
 // Concrete types are defined in the "metrics" package.
 type Metric interface {
         Info() MetricInfo
+        Metadata() MetricMetadata
 
         // SetFixedResetTime overrides the reset time for this metric.  Usually cells
         // take the current time when they're first assigned a value, but it can be
         // useful to override the reset time when tracking an external counter.
         SetFixedResetTime(t time.Time)
 }
 
 // DistributionMetric is the low-level interface provided by all distribution
 // metrics.  It has a Bucketer which is responsible for assigning buckets to
 // samples.  Concrete types are defined in the "metrics" package.
 type DistributionMetric interface {
         Metric
 
         Bucketer() *distribution.Bucketer
 }