Introduce ServiceWorker.EventDispatchingDelay 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 d650519ea4f0c634b685af0ec6e7178f5fb3cee0..6d69909e1aedf43d3f35213fbcfd2b38c5b9cc5b 100644
--- a/content/browser/service_worker/service_worker_metrics.h
+++ b/content/browser/service_worker/service_worker_metrics.h
@@ -210,6 +210,12 @@ class ServiceWorkerMetrics {
                                       size_t handled_events,
                                       size_t fired_events);
 
+  // Records the time taken between sending a FetchEvent IPC from the browser
+  // process to a Service Worker and executing the fetch event handler in the
+  // Service Worker.
+  static void RecordFetchEventDispatchingDelay(base::TimeDelta time,
+                                               Site site_for_metrics);
+
   // Records the precision of the speculative launch of Service Workers for
   // each navigation hint type when the worker is stopped. If there was no
   // main/sub frame fetch event fired on the worker, |frame_fetch_event_fired|