Use and add layout tests for BCP 47 language tag syntax validation.

Source/modules/notifications/ServiceWorkerRegistrationNotifications.cpp

Index: Source/modules/notifications/ServiceWorkerRegistrationNotifications.cpp
diff --git a/Source/modules/notifications/ServiceWorkerRegistrationNotifications.cpp b/Source/modules/notifications/ServiceWorkerRegistrationNotifications.cpp
index 5a0ad9a674c4d3542a9937b9e00c678d08d42a77..9b1558ab5b4b1bce8d9303de738a542df3ac372f 100644
--- a/Source/modules/notifications/ServiceWorkerRegistrationNotifications.cpp
+++ b/Source/modules/notifications/ServiceWorkerRegistrationNotifications.cpp
@@ -92,9 +92,11 @@ ScriptPromise ServiceWorkerRegistrationNotifications::showNotification(ScriptSta
             iconUrl = KURL();
     }
 
+    String lang = Platform::current()->isValidLocaleSyntax(options.lang()) ? options.lang() : "";
+
     WebNotificationData::Direction dir = options.dir() == "rtl" ? WebNotificationData::DirectionRightToLeft : WebNotificationData::DirectionLeftToRight;
     NavigatorVibration::VibrationPattern vibrate = NavigatorVibration::sanitizeVibrationPattern(options.vibrate());
-    WebNotificationData notification(title, dir, options.lang(), options.body(), options.tag(), iconUrl, vibrate, options.silent(), dataAsWireBytes);
+    WebNotificationData notification(title, dir, lang, options.body(), options.tag(), iconUrl, vibrate, options.silent(), dataAsWireBytes);
     WebNotificationShowCallbacks* callbacks = new CallbackPromiseAdapter<void, void>(resolver);
 
     SecurityOrigin* origin = executionContext->securityOrigin();