Only expose Notification.requestPermission() on the Window global.

Source/modules/notifications/Notification.idl

Index: Source/modules/notifications/Notification.idl
diff --git a/Source/modules/notifications/Notification.idl b/Source/modules/notifications/Notification.idl
index 142212bd3cf0ea480a0baa0f9e618322c2e7ab2c..dd08b230600be88e6d08748cc8d5bb66c47effaa 100644
--- a/Source/modules/notifications/Notification.idl
+++ b/Source/modules/notifications/Notification.idl
@@ -52,7 +52,7 @@ enum NotificationPermission {
     [CallWith=ExecutionContext, MeasureAs=NotificationPermission] static readonly attribute NotificationPermission permission;
 
     // TODO(peter): Only expose requestPermission() on the Window object. See https://crbug.com/442139.
-    [CallWith=ScriptState, MeasureAs=NotificationPermissionRequested] static Promise<NotificationPermission> requestPermission(optional NotificationPermissionCallback deprecatedCallback);
+    [CallWith=ScriptState, Exposed=Window, MeasureAs=NotificationPermissionRequested] static Promise<NotificationPermission> requestPermission(optional NotificationPermissionCallback deprecatedCallback);
 
     [RuntimeEnabled=NotificationExperimental] static readonly attribute unsigned long maxActions;