Make global callbacks usable outside appengine.

appengine/tsmon/middleware.go

Index: appengine/tsmon/middleware.go
diff --git a/appengine/tsmon/middleware.go b/appengine/tsmon/middleware.go
index c468002dfd6c18a71680d2f6b18abdad2a349be7..823699ebca28c1e8ca737fce0b8ce26720fa3148 100644
--- a/appengine/tsmon/middleware.go
+++ b/appengine/tsmon/middleware.go
@@ -144,6 +144,7 @@ func (s *State) checkSettings(c context.Context) (*tsmon.State, *tsmonSettings)
 	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")
 	}
@@ -341,6 +342,5 @@ func (s *State) doFlush(c context.Context, state *tsmon.State, settings *tsmonSe
 		return err
 	}
 
-	state.ResetGlobalCallbackMetrics(c)
 	return nil
 }