add longest_running_processor_microseconds metric

Kubernetes-commit: fd77aa5a41bbce7490dd4538c0d5743cb59b2be4

util/workqueue/metrics_test.go

@@ -94,6 +94,7 @@ type testMetricsProvider struct {
 	latency    testMetric
 	duration   testMetric
 	unfinished testMetric
+	longest    testMetric
 	retries    testMetric
 }
 
@@ -117,6 +118,10 @@ func (m *testMetricsProvider) NewUnfinishedWorkSecondsMetric(name string) Settab
 	return &m.unfinished
 }
 
+func (m *testMetricsProvider) NewLongestRunningProcessorMicrosecondsMetric(name string) SettableGaugeMetric {
+	return &m.longest
+}
+
 func (m *testMetricsProvider) NewRetriesMetric(name string) CounterMetric {
 	return &m.retries
 }
@@ -232,6 +237,9 @@ func TestMetrics(t *testing.T) {
 	if e, a := .001, mp.unfinished.gaugeValue(); e != a {
 		t.Errorf("expected %v, got %v", e, a)
 	}
+	if e, a := 1000.0, mp.longest.gaugeValue(); e != a {
+		t.Errorf("expected %v, got %v", e, a)
+	}
 
 	// Finish that one up
 	q.Done(i)