import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

toolkit/modules/PromiseMessage.jsm

@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
++ * License, v. 2.0. If a copy of the MPL was not distributed with this
++ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["PromiseMessage"];
+
+var msgId = 0;
+
+var PromiseMessage = {
+  send(messageManager, name, data = {}) {
+    const id = `${name}_${msgId++}`;
+
+    // Make a copy of data so that the caller doesn't see us setting 'id':
+    // To a new object, assign data's props, and then override the id.
+    const dataCopy = Object.assign({}, data, {id});
+
+    // Send the message.
+    messageManager.sendAsyncMessage(name, dataCopy);
+
+    // Return a promise that resolves when we get a reply (a message of the same name).
+    return new Promise(resolve => {
+      messageManager.addMessageListener(name, function listener(reply) {
+        if (reply.data.id !== id) {
+          return;
+        }
+        messageManager.removeMessageListener(name, listener);
+        resolve(reply);
+      });
+    });
+  }
+};