ServiceWorker: Keep the worker alive until FetchEvent.waitUntil settles

content/browser/service_worker/service_worker_metrics.h

Index: content/browser/service_worker/service_worker_metrics.h
diff --git a/content/browser/service_worker/service_worker_metrics.h b/content/browser/service_worker/service_worker_metrics.h
index 9be6cdb4a5147ff15ca6a9d2c40d4e7da42ee362..d4cc56e308d918760001d477b5c5fc5ba6890fe3 100644
--- a/content/browser/service_worker/service_worker_metrics.h
+++ b/content/browser/service_worker/service_worker_metrics.h
@@ -80,6 +80,13 @@ class ServiceWorkerMetrics {
   };
 
   // Used for UMA. Append-only.
+  // This class is used to indicate which event is fired/finished. Most events
+  // have only one request that starts the event and one response that finishes
+  // the event, but the fetch and the foreign fetch event have two responses, so
+  // there are two types of EventType to break down the measurement into two:
+  // FETCH/FOREIGN_FETCH and FETCH_WAITUNTIL/FOREIGN_FETCH_WAITUNTIL.
+  // Moreover, FETCH is separated into the four: MAIN_FRAME, SUB_FRAME,
+  // SHARED_WORKER and SUB_RESOURCE for more detailed UMA.
   enum class EventType {
     ACTIVATE = 0,
     INSTALL = 1,
@@ -97,6 +104,8 @@ class ServiceWorkerMetrics {
     FETCH_SUB_RESOURCE = 13,
     UNKNOWN = 14,  // Used when event type is not known.
     FOREIGN_FETCH = 15,
+    FETCH_WAITUNTIL = 16,
+    FOREIGN_FETCH_WAITUNTIL = 17,
     // Add new events to record here.
     NUM_TYPES
   };