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

LayoutTests/http/tests/notifications/notification-properties.html

Index: LayoutTests/http/tests/notifications/notification-properties.html
diff --git a/LayoutTests/http/tests/notifications/notification-properties.html b/LayoutTests/http/tests/notifications/notification-properties.html
index 38e05362905fb71bb7a4053658d9e66c1f03317f..e9603bcc2c63bfe55116466fcb3a9723df9efacb 100644
--- a/LayoutTests/http/tests/notifications/notification-properties.html
+++ b/LayoutTests/http/tests/notifications/notification-properties.html
@@ -58,6 +58,13 @@
             // Icon URLs should be returned in serialized form.
             assert_equals(serializedUrlNotification.icon, "http://example.com/");
 
+            var invalidLanguageNotification = new Notification("My Notification", {
+                lang: "invalid language"
+            });
+
+            // Invalid languages should be reset to an empty string.
+            assert_equals(invalidLanguageNotification.lang, "");
+
             var noTagNotification = new Notification("My Notification"),
                 emptyTagNotification = new Notification("My Notification", { tag: "" });