Add widget messaging stub.

src/WidgetMessaging.js

@@ -0,0 +1,41 @@
+/*
+Copyright 2016 OpenMarket Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export default class WidgetMessaging {
+    constructor() {
+    }
+
+    /**
+     * Register event listeners for the widget instance
+     * @param  {string} widgetId Unique widget identifier
+     * @return {undefined}
+     */
+    registerListeners(widgetId) {
+        if (widgetId) {
+            console.log("Register widget instance postmessage listeners");
+        } else {
+            console.error("Register widget event listeners - No widget ID specified!");
+        }
+    }
+
+    derigisterListeners(widgetId) {
+        if (widgetId) {
+            console.log("Register widget instance postmessage listeners");
+        } else {
+            console.error("Deregister widget event listerns - No widget ID specified!");
+        }
+    }
+}