IDL: make optional arguments (without default) explicit sometimes

Source/core/css/CSSStyleSheet.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. 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.
  *
  * 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.
  */
 
 #ifndef CSSStyleSheet_h
 #define CSSStyleSheet_h
 
+#include "bindings/core/v8/Optional.h"
 #include "core/css/CSSRule.h"
 #include "core/css/StyleSheet.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/TextPosition.h"
 
 namespace blink {
 
 class CSSCharsetRule;
 class CSSImportRule;
@@ skipping 30 matching lines @@
     virtual bool disabled() const OVERRIDE { return m_isDisabled; }
     virtual void setDisabled(bool) OVERRIDE;
 
     PassRefPtrWillBeRawPtr<CSSRuleList> cssRules();
     unsigned insertRule(const String& rule, unsigned index, ExceptionState&);
     unsigned insertRule(const String& rule, ExceptionState&); // Deprecated.
     void deleteRule(unsigned index, ExceptionState&);
 
     // IE Extensions
     PassRefPtrWillBeRawPtr<CSSRuleList> rules();
-    int addRule(const String& selector, const String& style, int index, ExceptionState&);
-    int addRule(const String& selector, const String& style, ExceptionState&);
+    int addRule(const String& selector, const String& style, Optional<int> index, ExceptionState&);
     void removeRule(unsigned index, ExceptionState& exceptionState) { deleteRule(index, exceptionState); }
 
     // For CSSRuleList.
     unsigned length() const;
     CSSRule* item(unsigned index);
 
     virtual void clearOwnerNode() OVERRIDE;
 
     virtual CSSRule* ownerRule() const OVERRIDE { return m_ownerRule; }
     virtual KURL baseURL() const OVERRIDE;
@@ skipping 81 matching lines @@
 {
     if (m_styleSheet)
         m_styleSheet->didMutateRules();
 }
 
 DEFINE_TYPE_CASTS(CSSStyleSheet, StyleSheet, sheet, sheet->isCSSStyleSheet(), sheet.isCSSStyleSheet());
 
 } // namespace
 
 #endif