Add UMA to record the ratio of how many fetch events are not handled

content/browser/service_worker/service_worker_version.cc

Index: content/browser/service_worker/service_worker_version.cc
diff --git a/content/browser/service_worker/service_worker_version.cc b/content/browser/service_worker/service_worker_version.cc
index 9504befa051be62a2107d6d13ce6525445130254..4299a26cbd2474f5077046f9852bc639a4601c13 100644
--- a/content/browser/service_worker/service_worker_version.cc
+++ b/content/browser/service_worker/service_worker_version.cc
@@ -366,6 +366,25 @@ bool IsInstalled(ServiceWorkerVersion::Status status) {
 const int ServiceWorkerVersion::kStartWorkerTimeoutMinutes = 5;
 const int ServiceWorkerVersion::kRequestTimeoutMinutes = 5;
 
+class ServiceWorkerVersion::ServiceWorkerEventMetrics {
+ public:
+  ServiceWorkerEventMetrics() {}
+  ~ServiceWorkerEventMetrics() {
+    ServiceWorkerMetrics::RecordEventStatus(fired_events, handled_events);
+  }
+
+  void RecordEventStatus(bool handled) {
+    ++fired_events;
+    if (handled)
+      ++handled_events;
+  }
+
+ private:
+  size_t fired_events = 0;
+  size_t handled_events = 0;
+  DISALLOW_COPY_AND_ASSIGN(ServiceWorkerEventMetrics);
+};
+
 ServiceWorkerVersion::ServiceWorkerVersion(
     ServiceWorkerRegistration* registration,
     const GURL& script_url,
@@ -379,6 +398,7 @@ ServiceWorkerVersion::ServiceWorkerVersion(
       context_(context),
       script_cache_map_(this, context),
       ping_state_(NOT_PINGING),
+      metrics_(new ServiceWorkerEventMetrics),
       weak_factory_(this) {
   DCHECK(context_);
   DCHECK(registration);
@@ -1185,6 +1205,10 @@ void ServiceWorkerVersion::OnFetchEventFinished(
     return;
   }
 
+  // TODO(kinuko): Record other event statuses too.
+  const bool handled = (result == SERVICE_WORKER_FETCH_EVENT_RESULT_RESPONSE);
+  metrics_->RecordEventStatus(handled);
+
   scoped_refptr<ServiceWorkerVersion> protect(this);
   callback->Run(SERVICE_WORKER_OK, result, response);
   RemoveCallbackAndStopIfRedundant(&fetch_callbacks_, request_id);