IDL: make optional arguments (without default) explicit sometimes

Source/core/html/HTMLInputElement.idl

Index: Source/core/html/HTMLInputElement.idl
diff --git a/Source/core/html/HTMLInputElement.idl b/Source/core/html/HTMLInputElement.idl
index 61a1ff60fa3d42fef94bb430e1ac34d414649f0e..2a81355ec578b8ed73547bab0e9e3c1c34187d85 100644
--- a/Source/core/html/HTMLInputElement.idl
+++ b/Source/core/html/HTMLInputElement.idl
@@ -64,8 +64,8 @@ interface HTMLInputElement : HTMLElement {
     [RaisesException=Setter, CustomElementCallbacks] attribute Date? valueAsDate;
     [RaisesException=Setter, CustomElementCallbacks] attribute unrestricted double valueAsNumber;
 
-    [RaisesException, CustomElementCallbacks] void stepUp(optional long n);
-    [RaisesException, CustomElementCallbacks] void stepDown(optional long n);
+    [RaisesException, CustomElementCallbacks] void stepUp(optional long n = 1);
+    [RaisesException, CustomElementCallbacks] void stepDown(optional long n = 1);
 
     [CustomElementCallbacks] attribute unsigned long width;
     readonly attribute boolean willValidate;
@@ -88,8 +88,8 @@ interface HTMLInputElement : HTMLElement {
                         optional DOMString selectionMode = null);
 
     [RaisesException, ImplementedAs=setSelectionRangeForBinding]
-    void setSelectionRange([Default=Undefined] optional long start,
-                           [Default=Undefined] optional long end,
+    void setSelectionRange(optional long start,
+                           optional long end,
                            optional DOMString direction);
 
     // Non-standard attributes