Revert of Make initEvent's first argument non-optional

third_party/WebKit/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,
@@ skipping 31 matching lines @@
     readonly attribute boolean cancelable;
     void preventDefault();
     readonly attribute boolean defaultPrevented;
 
     [MeasureAs=EventComposed] readonly attribute boolean composed;
 
     [Unforgeable] readonly attribute boolean isTrusted;
 
     [CallWith=ScriptState] readonly attribute DOMHighResTimeStamp timeStamp;
 
-    [Measure] void initEvent(DOMString type, optional boolean bubbles = false, optional boolean cancelable = false);
+    // FIXME: initEvent()'s arguments should not be optional.
+    [Measure] void initEvent([Default=Undefined] optional DOMString type,
+                             [Default=Undefined] optional boolean bubbles,
+                             [Default=Undefined] optional boolean cancelable);
 
     // Non-standard APIs
     [MeasureAs=EventSrcElement] readonly attribute EventTarget srcElement;
     [MeasureAs=EventReturnValue, CallWith=ScriptState, ImplementedAs=legacyReturnValue] attribute boolean returnValue;
     [MeasureAs=EventCancelBubble, CallWith=ScriptState] attribute boolean cancelBubble;
     [MeasureAs=EventPath, CallWith=ScriptState] readonly attribute EventTarget[] path;
 };