Introduce chrome://flags/#network-prediction-options-for-service-worker

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 ebc38fb71e7853f55a28dad6286c05d48fc7e30f..c3876337c7c0bff7b93780073fb1195ce0541735 100644
--- a/content/browser/service_worker/service_worker_metrics.cc
+++ b/content/browser/service_worker/service_worker_metrics.cc
@@ -84,6 +84,8 @@ std::string EventTypeToSuffix(ServiceWorkerMetrics::EventType event_type) {
       return "_BACKGROUND_FETCH_FAIL";
     case ServiceWorkerMetrics::EventType::BACKGROUND_FETCHED:
       return "_BACKGROUND_FETCHED";
+    case ServiceWorkerMetrics::EventType::PRECONNECT:
+      return "_PRECONNECT";
     case ServiceWorkerMetrics::EventType::NUM_TYPES:
       NOTREACHED() << static_cast<int>(event_type);
   }
@@ -317,6 +319,8 @@ const char* ServiceWorkerMetrics::EventTypeToString(EventType event_type) {
       return "Background Fetch Fail";
     case EventType::BACKGROUND_FETCHED:
       return "Background Fetched";
+    case EventType::PRECONNECT:
+      return "Preconnect";
     case EventType::NUM_TYPES:
       break;
   }
@@ -664,6 +668,8 @@ void ServiceWorkerMetrics::RecordEventDuration(EventType event,
                                  time);
       break;
 
+    case EventType::PRECONNECT:
+    // The predictior preconnection should not be sent as request events.
     case EventType::UNKNOWN:
     case EventType::NUM_TYPES:
       NOTREACHED() << "Invalid event type";