First step to refactor ServiceWorkerVersion to make event dispatching more modular.

content/browser/service_worker/service_worker_metrics.cc

Index: content/browser/service_worker/service_worker_metrics.cc
diff --git a/content/browser/service_worker/service_worker_metrics.cc b/content/browser/service_worker/service_worker_metrics.cc
index a900d4dfd5527d14a5892f50a48f6772e69d8528..95206ad8dd3bd91dbb00f30ea7b5ea7453989c65 100644
--- a/content/browser/service_worker/service_worker_metrics.cc
+++ b/content/browser/service_worker/service_worker_metrics.cc
@@ -168,12 +168,20 @@ void ServiceWorkerMetrics::RecordEventHandledRatio(EventType event,
     type = EVENT_HANDLED_ALL;
   else if (handled_events == 0)
     type = EVENT_HANDLED_NONE;
+
   // For now Fetch is the only type that is recorded.
-  DCHECK_EQ(EVENT_TYPE_FETCH, event);
+  if (event != EventType::FETCH)
+    return;
   UMA_HISTOGRAM_ENUMERATION("ServiceWorker.EventHandledRatioType.Fetch", type,
                             NUM_EVENT_HANDLED_RATIO_TYPE);
 }
 
+void ServiceWorkerMetrics::RecordEventTimeout(EventType event) {
+  UMA_HISTOGRAM_ENUMERATION("ServiceWorker.RequestTimeouts.Count",
+                            static_cast<int>(event),
+                            static_cast<int>(EventType::NUM_TYPES));
+}
+
 void ServiceWorkerMetrics::RecordFetchEventStatus(
     bool is_main_resource,
     ServiceWorkerStatusCode status) {