Add messageerror event handler

third_party/WebKit/Source/modules/broadcastchannel/BroadcastChannel.idl

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://html.spec.whatwg.org/multipage/comms.html#broadcastchannel
 
 [
     Constructor(DOMString name),
     ConstructorCallWith=ExecutionContext,
     RaisesException=Constructor,
     RuntimeEnabled=BroadcastChannel,
     Exposed=(Window,Worker),
     ActiveScriptWrappable,
     DependentLifetime,
     Measure,
 ] interface BroadcastChannel : EventTarget {
     readonly attribute DOMString name;
 
     [RaisesException, Measure] void postMessage(any message);
     [Measure] void close();
 
     // event handlers
     attribute EventHandler onmessage;
+    attribute EventHandler onmessageerror;
 };