Sync the Event, EventTarget and CustomEvent interfaces with the spec

Source/core/events/EventTarget.idl

 /*
  * Copyright (C) 2006, 2007 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.
  */
 
+// https://dom.spec.whatwg.org/#interface-eventtarget
+
 [
     CheckSecurity=Window,
     Custom=ToV8,
     WillBeGarbageCollected,
     Exposed=(Window,Worker)
 ] interface EventTarget {
     // FIXME: first 2 args should be required, but throwing TypeError breaks
     // legacy content.  http://crbug.com/353484
-    void addEventListener(optional DOMString? type,
-                          optional EventListener listener,
-                          optional boolean useCapture);
-    void removeEventListener(optional DOMString? type,
-                             optional EventListener listener,
-                             optional boolean useCapture);
+    // FIXME: type should not be nullable.
+    // FIXME: capture should have a default value false.
+    void addEventListener(optional DOMString? type, optional EventListener? listener, optional boolean capture);
+    void removeEventListener(optional DOMString? type, optional EventListener? listener, optional boolean capture);
     [RaisesException] boolean dispatchEvent(Event event);
 };