Added unit annotation supports onto tsmon in go.

common/tsmon/types/cell.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/field"
 )
 
 // Cell is the smallest unit of data recorded by tsmon.  Metrics can be
 // thought of as multi-dimensional maps (with fields defining the dimensions) -
 // a Cell is one value in that map, with information about its fields and its
 // type.
 type Cell struct {
         MetricInfo
+        MetricMetadata
         CellData
 }
 
 // MetricInfo contains the definition of a metric.
 type MetricInfo struct {
         Name        string
         Description string
         Fields      []field.Field
         ValueType   ValueType
 }
 
+// MetricMetadata contains user-provided metadata for a metric.
+type MetricMetadata struct {
+        Units MetricDataUnits // the unit of recorded data for a given metric.
+}
+
 // CellData contains the value of a single cell.
 type CellData struct {
         FieldVals []interface{}
         Target    Target
         ResetTime time.Time
         Value     interface{}
 }