Add UMA for how long service workers run for.

content/browser/service_worker/service_worker_version.h

 // Copyright 2013 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_VERSION_H_
 #define CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_VERSION_H_
 
 #include <stdint.h>
 
 #include <functional>
@@ skipping 116 matching lines @@
                                         int source_identifier,
                                         int message_level,
                                         const base::string16& message,
                                         int line_number,
                                         const GURL& source_url) {}
     virtual void OnControlleeAdded(ServiceWorkerVersion* version,
                                    ServiceWorkerProviderHost* provider_host) {}
     virtual void OnControlleeRemoved(ServiceWorkerVersion* version,
                                      ServiceWorkerProviderHost* provider_host) {
     }
+    virtual void OnDevToolsAttached(ServiceWorkerVersion* version) {}

[nhiroki, 2017/02/28 08:50:07]

Maybe is this no longer necessary?

     virtual void OnNoControllees(ServiceWorkerVersion* version) {}
     virtual void OnNoWork(ServiceWorkerVersion* version) {}
     virtual void OnCachedMetadataUpdated(ServiceWorkerVersion* version) {}
 
    protected:
     virtual ~Listener() {}
   };
 
   ServiceWorkerVersion(ServiceWorkerRegistration* registration,
                        const GURL& script_url,
@@ skipping 767 matching lines @@
 
   // At this point |this| can have been deleted, so don't do anything other
   // than returning.
 
   return true;
 }
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_VERSION_H_