Make more [TreatNullAs=NullString] DOMString arguments nullable

Source/core/dom/Document.idl

 /*
  * Copyright (C) 2006, 2007, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2007 Samuel Weinig <sam@webkit.org>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 80 matching lines @@
     CSSStyleDeclaration getOverrideStyle([Default=Undefined] optional Element element,
                                          [Default=Undefined] optional DOMString pseudoElement);
 
     // DOM 4
     readonly attribute DOMString contentType;
 
     // Common extensions
     [CustomElementCallbacks]
     boolean            execCommand([Default=Undefined] optional DOMString command,
                                    [Default=Undefined] optional boolean userInterface,
-                                   [TreatNullAs=NullString, TreatUndefinedAs=NullString,Default=Undefined] optional DOMString value);
+                                   [TreatUndefinedAs=NullString, Default=Undefined] optional DOMString? value);

[Jens Widell, 2014/07/02 12:42:20]

If we fix http://crbug.com/335871, then in terms of behavior, this could just be
"optional DOMString? value = null". (CG would differ somewhat, though.)

The same probably goes for various arguments touched in this CL that don't have
[Default=Undefined], but in those cases it depends on how the C++ side is
implemented.

[haraken, 2014/07/02 12:50:27]

Yeah, it's worth fixing.

 
     boolean            queryCommandEnabled([Default=Undefined] optional DOMString command);
     boolean            queryCommandIndeterm([Default=Undefined] optional DOMString command);
     boolean            queryCommandState([Default=Undefined] optional DOMString command);
     boolean            queryCommandSupported([Default=Undefined] optional DOMString command);
     DOMString          queryCommandValue([Default=Undefined] optional DOMString command);
 
     // Moved down from HTMLDocument
              [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString dir;
              [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString designMode;
@@ skipping 104 matching lines @@
     // TODO(davidben): This is a property so attaching a deprecation warning results in false positives when outputting
     // document in the console. It's possible http://crbug.com/43394 will resolve this.
     [MeasureAs=PrefixedPageVisibility, ImplementedAs=visibilityState] readonly attribute DOMString webkitVisibilityState;
     [MeasureAs=PrefixedPageVisibility, ImplementedAs=hidden] readonly attribute boolean webkitHidden;
 
     readonly attribute HTMLScriptElement currentScript;
 };
 
 Document implements GlobalEventHandlers;
 Document implements ParentNode;