service worker: Attribute purpose to start worker attempts for UMA

content/browser/service_worker/service_worker_registration.cc

Index: content/browser/service_worker/service_worker_registration.cc
diff --git a/content/browser/service_worker/service_worker_registration.cc b/content/browser/service_worker/service_worker_registration.cc
index e1e6e5d1822761c4b0914478fdc93e89b7911232..f476c73d2f343986df2b60159b05058b7f4bb630 100644
--- a/content/browser/service_worker/service_worker_registration.cc
+++ b/content/browser/service_worker/service_worker_registration.cc
@@ -290,7 +290,8 @@ void ServiceWorkerRegistration::ActivateWaitingVersion() {
       base::Bind(&ServiceWorkerRegistration::DispatchActivateEvent, this,
                  activating_version),
       base::Bind(&ServiceWorkerRegistration::OnActivateEventFinished, this,
-                 activating_version));
+                 activating_version),
+      ServiceWorkerMetrics::EventType::ACTIVATE);
 }
 
 void ServiceWorkerRegistration::DeleteVersion(