Move HTMLInputElement method argument defaults into IDL file

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..d53dd5bdc3f779b2902bbeaf7d938c29b450b390 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;
@@ -85,7 +85,7 @@ interface HTMLInputElement : HTMLElement {
     [RaisesException] void setRangeText(DOMString replacement,
                         unsigned long start,
                         unsigned long end,
-                        optional DOMString selectionMode = null);
+                        optional DOMString selectionMode = "preserve");
 
     [RaisesException, ImplementedAs=setSelectionRangeForBinding]
     void setSelectionRange([Default=Undefined] optional long start,