[ios] Use args destructuring in Mojo test promise.

ios/web/test/data/mojo_test.js

 // 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.
 
 // This module provides the test page for WebUIMojoTest. Once the page is
 // loaded it sends "syn" message to the native code. Once page receives "ack"
 // from the native code, the page then sends "fin". Test succeeds only when
 // "fin" is received by the native page. Refer to
 // ios/web/webui/web_ui_mojo_inttest.mm for testing code.
 
@@ skipping 38 matching lines @@
  * @return {!Promise} Fires when DOMContentLoaded event is received.
  */
 function whenDomContentLoaded() {
   return new Promise(function(resolve, reject) {
     document.addEventListener('DOMContentLoaded', resolve);
   });
 }
 
 function main() {
   Promise.all([
-    whenDomContentLoaded(), getBrowserProxy()
-  ]).then(function(results) {
-    var browserProxy = results[1];
+    getBrowserProxy(), whenDomContentLoaded()
+  ]).then(function([browserProxy]) {
     // Send "syn" so native code should reply with "ack".
     browserProxy.handleJsMessage('syn');
   });
 }
 main();