ServiceWorker: Introduce ServiceWorkerMessageEvent to replace MessageEvent (3/3).

Source/modules/serviceworkers/ServiceWorkerMessageEvent.idl

Index: Source/modules/serviceworkers/ServiceWorkerMessageEvent.idl
diff --git a/Source/modules/serviceworkers/ServiceWorkerMessageEvent.idl b/Source/modules/serviceworkers/ServiceWorkerMessageEvent.idl
new file mode 100644
index 0000000000000000000000000000000000000000..b94566e69a39a6cdf5c11b443595d058767964c6
--- /dev/null
+++ b/Source/modules/serviceworkers/ServiceWorkerMessageEvent.idl
@@ -0,0 +1,17 @@
+// Copyright 2015 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://slightlyoff.github.io/ServiceWorker/spec/service_worker/#serviceworkermessage-event-section
+
+[
+    Constructor(DOMString type, optional ServiceWorkerMessageEventInit eventInitDict),
+    Exposed=(Window, Worker),
+    RuntimeEnabled=ServiceWorker,
+] interface ServiceWorkerMessageEvent : Event {
+    readonly attribute DOMString origin;
+    readonly attribute DOMString lastEventId;
+    readonly attribute (ServiceWorker or MessagePort)? source;
+    [Custom=Getter] readonly attribute any data;
+    readonly attribute MessagePort[] ports;
+};