Replace many [TreatReturnedNullStringAs=Null] with nullable DOMString

Source/core/css/CSSStyleDeclaration.idl

 /*
  * Copyright (C) 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 // Introduced in DOM Level 2:
 [
     DependentLifetime,
     WillBeGarbageCollected
 ] interface CSSStyleDeclaration {
-             [TreatReturnedNullStringAs=Null, TreatNullAs=NullString, RaisesException=Setter] attribute DOMString        cssText;
+    [RaisesException=Setter] attribute DOMString?       cssText;
 
-    [TreatReturnedNullStringAs=Null] DOMString          getPropertyValue([Default=Undefined] optional DOMString propertyName);
-    [TreatReturnedNullStringAs=Null, RaisesException] DOMString          removeProperty([Default=Undefined] optional DOMString propertyName);
-    [TreatReturnedNullStringAs=Null] DOMString          getPropertyPriority([Default=Undefined] optional DOMString propertyName);
-     [RaisesException] void setProperty([Default=Undefined] optional DOMString propertyName,
-                                    [TreatNullAs=NullString,Default=Undefined] optional DOMString value,
-                                    [TreatNullAs=NullString] optional DOMString priority = null);
+    DOMString?          getPropertyValue([Default=Undefined] optional DOMString propertyName);
+    [RaisesException] DOMString?          removeProperty([Default=Undefined] optional DOMString propertyName);
+    DOMString?          getPropertyPriority([Default=Undefined] optional DOMString propertyName);
+    [RaisesException] void setProperty([Default=Undefined] optional DOMString propertyName,
+                                       [TreatNullAs=NullString,Default=Undefined] optional DOMString value,
+                                       [TreatNullAs=NullString] optional DOMString priority = null);
 
     readonly attribute unsigned long    length;
     getter DOMString          item([Default=Undefined] optional unsigned long index);
     [Custom=PropertyGetter|PropertyEnumerator|PropertyQuery] getter (DOMString or float) (DOMString name);
     [Custom] setter void (DOMString propertyName, [TreatNullAs=NullString] DOMString propertyValue);
     readonly attribute CSSRule          parentRule;
 
     // Deprecated as of 2003: http://lists.w3.org/Archives/Public/www-style/2003Oct/0347.html
     // FIXME: This should be DeprecateAs=, but currently too many LayoutTests use
     // this function and would need CONSOLE: message rebaselines!
     [MeasureAs=CSSStyleDeclarationGetPropertyCSSValue] CSSValue           getPropertyCSSValue([Default=Undefined] optional DOMString propertyName);
 };