collect metric results so that probe latecy can be reported in /debug…

…/metrics

Signed-off-by: Shlomi Noach <[email protected]>

go/vt/vttablet/tabletserver/throttle/throttler.go

@@ -932,7 +932,7 @@ func (throttler *Throttler) generateTabletProbeFunction(scope base.Scope, tmClie
 // readSelfThrottleMetricsInternal rreads all registsred self metrics on this tablet (or backend MySQL server).
 // This is the actual place where metrics are read, to be later aggregated and/or propagated to other tablets.
 func (throttler *Throttler) readSelfThrottleMetricsInternal(ctx context.Context) base.ThrottleMetrics {
-
+	result := make(base.ThrottleMetrics)
 	writeMetric := func(metric *base.ThrottleMetric) {
 		select {
 		case <-ctx.Done():
@@ -960,8 +960,9 @@ func (throttler *Throttler) readSelfThrottleMetricsInternal(ctx context.Context)
 		metric.Alias = throttler.tabletAlias
 
 		go writeMetric(metric)
+		result[metricName] = metric
 	}
-	return nil
+	return result
 }
 
 func (throttler *Throttler) collectSelfMetrics(ctx context.Context) {