Remove CSSRule.UNKNOWN_RULE and CSSUnknownRule interface

Source/core/css/CSSRule.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.
  */
 
 // http://dev.w3.org/csswg/cssom/#the-cssrule-interface
 
 [
     DependentLifetime,
     WillBeGarbageCollected,
 ] interface CSSRule {
-    // TODO(philipj): UNKNOWN_RULE has been removed from the spec.
-    const unsigned short UNKNOWN_RULE = 0;
     const unsigned short STYLE_RULE = 1;
     const unsigned short CHARSET_RULE = 2;
     const unsigned short IMPORT_RULE = 3;
     const unsigned short MEDIA_RULE = 4;
     const unsigned short FONT_FACE_RULE = 5;
     const unsigned short PAGE_RULE = 6;
     // TODO(philipj): Implement CSSMarginRule.
     // const unsigned short MARGIN_RULE = 9;
     // TODO(philipj): Implement CSSNamespaceRule. crbug.com/389549
     // const unsigned short NAMESPACE_RULE = 10;
@@ skipping 12 matching lines @@
     const unsigned short SUPPORTS_RULE = 12;
 
     // CSS Device Adaptation
     // http://dev.w3.org/csswg/css-device-adapt/#css-rule-interface
     [RuntimeEnabled=CSSViewport] const unsigned short VIEWPORT_RULE = 15;
 
     // Non-standard APIs
     const unsigned short WEBKIT_KEYFRAMES_RULE = 7;
     const unsigned short WEBKIT_KEYFRAME_RULE = 8;
 };