IDL: make optional arguments (without default) explicit sometimes

Source/core/frame/WindowTimers.idl

Index: Source/core/frame/WindowTimers.idl
diff --git a/Source/core/frame/WindowTimers.idl b/Source/core/frame/WindowTimers.idl
index 47f394fc249175fc435305994fd8e972a4f1f1ca..2014ec5a248dbc9cf0b3e6fcb76781af25b49db0 100644
--- a/Source/core/frame/WindowTimers.idl
+++ b/Source/core/frame/WindowTimers.idl
@@ -38,8 +38,8 @@
     // FIXME: would be clearer as a union type, like:
     // typedef (Function or DOMString) Handler
     // Needs spec update and better union support: http://crbug.com/240176
-    [Custom] long setTimeout(any handler, [Default=Undefined] optional long timeout);
-    void clearTimeout([Default=Undefined] optional long handle);
-    [Custom] long setInterval(any handler, [Default=Undefined] optional long timeout);
-    void clearInterval([Default=Undefined] optional long handle);
+    [Custom] long setTimeout(any handler, optional long timeout);
+    void clearTimeout(optional long handle);
+    [Custom] long setInterval(any handler, optional long timeout);
+    void clearInterval(optional long handle);
 };