Move HTMLInputElement method argument defaults into IDL file

Source/core/html/HTMLInputElement.idl

 /*
  * Copyright (C) 2006, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 46 matching lines @@
     [Reflect, URL] attribute DOMString src;
     [Reflect] attribute DOMString step;
     [CustomElementCallbacks] attribute DOMString type; // readonly dropped as part of DOM level 2
     [Reflect=value, CustomElementCallbacks] attribute DOMString defaultValue;
     [Reflect] attribute DOMString useMap;
     // See the discussion in https://bugs.webkit.org/show_bug.cgi?id=100085
     [TreatNullAs=EmptyString, RaisesException=Setter, CustomElementCallbacks] attribute DOMString value;
     [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;
     readonly attribute ValidityState validity;
     readonly attribute DOMString validationMessage;
     boolean checkValidity();
     void setCustomValidity([TreatUndefinedAs=NullString] DOMString? error);
 
     readonly attribute NodeList labels;
 
     void select();
     [RaisesException, ImplementedAs=selectionStartForBinding] attribute long selectionStart;
     [RaisesException, ImplementedAs=selectionEndForBinding] attribute long selectionEnd;
     [RaisesException, ImplementedAs=selectionDirectionForBinding] attribute DOMString selectionDirection;
 
     [RaisesException] void setRangeText(DOMString replacement);
     [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,
                            [Default=Undefined] optional long end,
                            optional DOMString direction);
 
     // Non-standard attributes
     [Reflect, MeasureAs=PrefixedDirectoryAttribute] attribute boolean webkitdirectory;
     [Reflect, MeasureAs=IncrementalAttribute] attribute boolean incremental;
 
     // See http://www.w3.org/TR/html-media-capture/
     [RuntimeEnabled=MediaCapture, Reflect] attribute boolean capture;
 };