Introduce luci-go components version metric.

appengine/tsmon/standardmetrics.go

 // Copyright 2016 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 tsmon
 
 import (
         "golang.org/x/net/context"
 
         "github.com/luci/gae/service/module"
         "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/common/tsmon"
         "github.com/luci/luci-go/common/tsmon/metric"
         "github.com/luci/luci-go/common/tsmon/runtimestats"
+        "github.com/luci/luci-go/common/tsmon/versions"
 )
 
 var (
         defaultVersion = metric.NewCallbackString(
                 "appengine/default_version",
                 "Name of the version currently marked as default.",
                 nil)
 )
 
 // collectGlobalMetrics populates service-global metrics.
 //
 // Called by tsmon from inside /housekeeping cron handler. Metrics reported must
 // not depend on the state of the particular process that happens to report
 // them.
 func collectGlobalMetrics(c context.Context) {
         version, err := module.DefaultVersion(c, "")
         if err != nil {
                 logging.Errorf(c, "Error getting default appengine version: %s", err)
                 defaultVersion.Set(c, "(unknown)")
         } else {
                 defaultVersion.Set(c, version)
         }
 }
 
 // collectProcessMetrics populates per-process metrics.
 //
 // It is called by each individual process right before flushing the metrics.
 func collectProcessMetrics(c context.Context, s *tsmonSettings) {
+        versions.Report(c)
         if s.ReportRuntimeStats {
                 runtimestats.Report(c)
         }
 }
 
 func init() {
         tsmon.RegisterGlobalCallback(collectGlobalMetrics, defaultVersion)
 }