service worker: Add UMA for navigation preload response timing.

content/browser/service_worker/service_worker_metrics.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_METRICS_H_
 #define CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_METRICS_H_
 
 #include <stddef.h>
 
 #include "base/macros.h"
@@ skipping 299 matching lines @@
 
   // Records the result of a start attempt that occurred after the worker had
   // failed |failure_count| consecutive times.
   static void RecordStartStatusAfterFailure(int failure_count,
                                             ServiceWorkerStatusCode status);
 
   // Records the size of Service-Worker-Navigation-Preload header when the
   // navigation preload request is to be sent.
   static void RecordNavigationPreloadRequestHeaderSize(size_t size);
 
+  // Records timings for the navigation preload response and how
+  // it compares to starting the worker.
+  // |worker_start| is the time it took to prepare an activated and running
+  // worker to receive the fetch event. |initial_worker_status| and
+  // |start_situation| describe the preparation needed.
+  // |response_start| is the time it took until the navigation preload response
+  // started.
+  CONTENT_EXPORT static void RecordNavigationPreloadResponse(
+      base::TimeDelta worker_start,
+      base::TimeDelta response_start,
+      EmbeddedWorkerStatus initial_worker_status,
+      StartSituation start_situation);
+
   // Records the result of trying to handle a request for a service worker
   // script.
   static void RecordContextRequestHandlerStatus(
       ServiceWorkerContextRequestHandler::CreateJobStatus status,
       bool is_installed,
       bool is_main_script);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ServiceWorkerMetrics);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_METRICS_H_