Implement the ServiceWorkerRegistration.showNotification() method.

Source/modules/modules.gypi

 {
   'includes': [
     '../core/core_generated.gypi',
     'modules_generated.gypi',
   ],
   'variables': {
     # Experimental hooks for embedder to provide extra IDL and source files.
     #
     # Note: this is not a supported API. If you rely on this, you will be broken
     # from time to time as the code generator changes in backward incompatible
@@ skipping 225 matching lines @@
       'indexeddb/WorkerGlobalScopeIndexedDatabase.idl',
       'mediasource/HTMLVideoElementMediaSource.idl',
       'mediasource/URLMediaSource.idl',
       'mediastream/NavigatorMediaStream.idl',
       'mediastream/URLMediaStream.idl',
       'mediastream/WindowMediaStream.idl',
       'navigatorcontentutils/NavigatorContentUtils.idl',
       'netinfo/NavigatorNetworkInformation.idl',
       'netinfo/WorkerNavigatorNetworkInformation.idl',
       'notifications/ServiceWorkerGlobalScopeNotifications.idl',
+      'notifications/ServiceWorkerRegistrationNotifications.idl',
       'performance/SharedWorkerPerformance.idl',
       'performance/WorkerGlobalScopePerformance.idl',
       'presentation/NavigatorPresentation.idl',
       'push_messaging/NavigatorPushManager.idl',
       'push_messaging/ServiceWorkerGlobalScopePush.idl',
       'quota/NavigatorStorageQuota.idl',
       'quota/WindowQuota.idl',
       'quota/WorkerNavigatorStorageQuota.idl',
       'screen_orientation/ScreenScreenOrientation.idl',
       'serviceworkers/NavigatorServiceWorker.idl',
@@ skipping 482 matching lines @@
       'notifications/Notification.h',
       'notifications/NotificationClient.h',
       'notifications/NotificationController.cpp',
       'notifications/NotificationController.h',
       'notifications/NotificationEvent.cpp',
       'notifications/NotificationEvent.h',
       'notifications/NotificationPermissionCallback.h',
       'notifications/NotificationPermissionClient.cpp',
       'notifications/NotificationPermissionClient.h',
       'notifications/ServiceWorkerGlobalScopeNotifications.h',
+      'notifications/ServiceWorkerRegistrationNotifications.cpp',
+      'notifications/ServiceWorkerRegistrationNotifications.h',
       'performance/SharedWorkerPerformance.cpp',
       'performance/WorkerGlobalScopePerformance.cpp',
       'performance/WorkerGlobalScopePerformance.h',
       'performance/WorkerPerformance.cpp',
       'performance/WorkerPerformance.h',
       'presentation/NavigatorPresentation.cpp',
       'presentation/NavigatorPresentation.h',
       'presentation/Presentation.cpp',
       'presentation/Presentation.h',
       'presentation/PresentationSession.cpp',
@@ skipping 355 matching lines @@
       'serviceworkers/CacheTest.cpp',
       'serviceworkers/FetchResponseDataTest.cpp',
       'serviceworkers/RequestTest.cpp',
       'serviceworkers/ResponseTest.cpp',
       'serviceworkers/ServiceWorkerContainerTest.cpp',
       'websockets/DOMWebSocketTest.cpp',
       'websockets/DocumentWebSocketChannelTest.cpp',
     ],
   },
 }