Document the tracking bugs of some straight-forward IDL bugs

Source/core/css/CSSUnknownRule.idl

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  * 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.
  */
 
 // The CSSUnknownRule interface was introduced in DOM Level 2 Style, but has
 // been removed in CSSOM:
 // http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSUnknownRule
 // http://dev.w3.org/csswg/cssom/
 //
-// TODO(philipj): Remove CSSUnknownRule.
+// TODO(philipj): Remove CSSUnknownRule. crbug.com/496383
 
 interface CSSUnknownRule : CSSRule {
 };