Push API: rename registration to subscription.

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 112 matching lines @@
       'notifications/NotificationEvent.idl',
       'notifications/NotificationPermissionCallback.idl',
       'performance/WorkerPerformance.idl',
       'permissions/Permissions.idl',
       'permissions/PermissionStatus.idl',
       'presentation/Presentation.idl',
       'presentation/PresentationSession.idl',
       'push_messaging/PushEvent.idl',
       'push_messaging/PushManager.idl',
       'push_messaging/PushMessageData.idl',
-      'push_messaging/PushRegistration.idl',
+      'push_messaging/PushSubscription.idl',
       'quota/DeprecatedStorageInfo.idl',
       'quota/DeprecatedStorageQuota.idl',
       'quota/StorageErrorCallback.idl',
       'quota/StorageInfo.idl',
       'quota/StorageQuota.idl',
       'quota/StorageQuotaCallback.idl',
       'quota/StorageUsageCallback.idl',
       'screen_orientation/ScreenOrientation.idl',
       'serviceworkers/Cache.idl',
       'serviceworkers/CacheStorage.idl',
@@ skipping 728 matching lines @@
       'push_messaging/PushError.cpp',
       'push_messaging/PushError.h',
       'push_messaging/PushEvent.cpp',
       'push_messaging/PushEvent.h',
       'push_messaging/PushManager.cpp',
       'push_messaging/PushManager.h',
       'push_messaging/PushMessageData.cpp',
       'push_messaging/PushMessageData.h',
       'push_messaging/PushPermissionStatusCallbacks.cpp',
       'push_messaging/PushPermissionStatusCallbacks.h',
-      'push_messaging/PushRegistration.cpp',
-      'push_messaging/PushRegistration.h',
-      'push_messaging/PushRegistrationCallbacks.cpp',
-      'push_messaging/PushRegistrationCallbacks.h',
+      'push_messaging/PushSubscription.cpp',
+      'push_messaging/PushSubscription.h',
+      'push_messaging/PushSubscriptionCallbacks.cpp',
+      'push_messaging/PushSubscriptionCallbacks.h',
       'push_messaging/ServiceWorkerGlobalScopePush.h',
       'push_messaging/ServiceWorkerRegistrationPush.cpp',
       'push_messaging/ServiceWorkerRegistrationPush.h',
       'quota/DOMWindowQuota.cpp',
       'quota/DOMWindowQuota.h',
       'quota/DeprecatedStorageInfo.cpp',
       'quota/DeprecatedStorageInfo.h',
       'quota/DeprecatedStorageQuota.cpp',
       'quota/DeprecatedStorageQuota.h',
       'quota/DeprecatedStorageQuotaCallbacksImpl.cpp',
@@ skipping 323 matching lines @@
       'indexeddb/IDBKeyPathTest.cpp',
       'indexeddb/IDBRequestTest.cpp',
       'indexeddb/IDBTransactionTest.cpp',
       'serviceworkers/CacheTest.cpp',
       'serviceworkers/ServiceWorkerContainerTest.cpp',
       'websockets/DOMWebSocketTest.cpp',
       'websockets/DocumentWebSocketChannelTest.cpp',
     ],
   },
 }