Add UMA for how long service workers run for.

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 <map>
 #include <set>
@@ skipping 336 matching lines @@
       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);
 
+  static void RecordRuntime(base::TimeDelta time);
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ServiceWorkerMetrics);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_METRICS_H_