Introduce ServiceWorker.ActivatedWorkerPreparationForMainFrame.Time UMA.

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 aca36c9e351e3bebeceacdef260a0b22e1c7df25..4e5dafdbcab65dc839b6594965371e711008d0e6 100644
--- a/content/browser/service_worker/service_worker_metrics.h
+++ b/content/browser/service_worker/service_worker_metrics.h
@@ -8,6 +8,7 @@
 #include <stddef.h>
 
 #include "base/macros.h"
+#include "content/browser/service_worker/embedded_worker_status.h"
 #include "content/browser/service_worker/service_worker_database.h"
 #include "content/common/service_worker/service_worker_types.h"
 #include "third_party/WebKit/public/platform/modules/serviceworker/WebServiceWorkerResponseError.h"
@@ -161,6 +162,13 @@ class ServiceWorkerMetrics {
                                     StartSituation start_situation,
                                     EventType purpose);
 
+  // Records the time taken to prepare an activated Service Worker for a main
+  // frame fetch.
+  static void RecordActivatedWorkerPreparationTimeForMainFrame(
+      base::TimeDelta time,
+      EmbeddedWorkerStatus initial_worker_status,
+      StartSituation start_situation);
+
   // Records the result of trying to stop a worker.
   static void RecordWorkerStopped(StopStatus status);