Make global callbacks usable outside appengine.

appengine/tsmon/middleware.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 (
         "fmt"
         "net/http"
         "net/url"
@@ skipping 126 matching lines @@
 
         // 'settings' or 'state' has changed. Reinitialize tsmon as needed under
         // the write lock.
         s.lock.Lock()
         defer s.lock.Unlock()
 
         // First call to 'checkSettings' ever?
         if s.state == nil {
                 s.state = state
                 s.state.M = monitor.NewNilMonitor() // doFlush uses its own monitor
+                s.state.InvokeGlobalCallbacksOnFlush = false
         } else if state != s.state {
                 panic("tsmon state in the context was unexpectedly changed between requests")
         }
 
         switch {
         case !bool(s.lastSettings.Enabled) && bool(settings.Enabled):
                 s.enableTsMon(c)
         case bool(s.lastSettings.Enabled) && !bool(settings.Enabled):
                 s.disableTsMon(c)
         }
@@ skipping 177 matching lines @@
                 if err != nil {
                         return err
                 }
         }
 
         defer mon.Close()
         if err = state.Flush(c, mon); err != nil {
                 return err
         }
 
-        state.ResetGlobalCallbackMetrics(c)
         return nil
 }