Revert "Add [WillBeGarbageCollected] to Event.idl"

Source/core/events/Event.idl

 /*
  * Copyright (C) 2006, 2007, 2009, 2011 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:
 [
-    WillBeGarbageCollected,
     Custom=Wrap,
     EventConstructor,
 ] interface Event {
 
     // DOM PhaseType
     const unsigned short NONE                = 0;
     const unsigned short CAPTURING_PHASE     = 1;
     const unsigned short AT_TARGET           = 2;
     const unsigned short BUBBLING_PHASE      = 3;
 
@@ skipping 35 matching lines @@
 
     // IE Extensions
     readonly attribute EventTarget      srcElement;
     [ImplementedAs=legacyReturnValue, DeprecateAs=EventReturnValue] attribute boolean returnValue;
              attribute boolean          cancelBubble;
 
     [RuntimeEnabled=ShadowDOM] readonly attribute NodeList path;
 
     [Custom=Getter] readonly attribute Clipboard clipboardData;
 };