Mark anonymous indexed getters argument as mandatory

Source/core/html/HTMLFormControlsCollection.idl

Index: Source/core/html/HTMLFormControlsCollection.idl
diff --git a/Source/core/html/HTMLFormControlsCollection.idl b/Source/core/html/HTMLFormControlsCollection.idl
index 30307382a5eae3238b4979808343649020533222..e7b757e0f9b74c69c16369f1299428a42fdbda95 100644
--- a/Source/core/html/HTMLFormControlsCollection.idl
+++ b/Source/core/html/HTMLFormControlsCollection.idl
@@ -22,7 +22,7 @@
     GenerateIsReachable=ownerNode,
     DependentLifetime
 ] interface HTMLFormControlsCollection : HTMLCollection {
-    [ImplementedAs=item] getter Node([Default=Undefined] optional unsigned long index);
+    [ImplementedAs=item] getter Node(unsigned long index);
     [Custom] Node namedItem([Default=Undefined] optional DOMString name);
     [ImplementedAs=namedGetter, NotEnumerable] getter (RadioNodeList or Node)(DOMString name);
 };