Fix loadAssetsOnIdle not loading when document.readyState is 'interactive'.

ui/login/resource_loader.js

 // Copyright 2014 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.
 
 /**
  * @fileoverview Deferred resource loader for OOBE/Login screens.
  */
 
 cr.define('cr.ui.login.ResourceLoader', function() {
   'use strict';
@@ skipping 177 matching lines @@
   /**
    * Load an asset bundle after the document has been loaded and Chrome is idle.
    * @param {string} id Identifier for the asset bundle to load.
    * @param {function()=} callback Function to invoke when done loading.
    * @param {number=} opt_idleTimeoutMs The maximum amount of time to wait for
    * an idle notification.
    */
   function loadAssetsOnIdle(id, callback, opt_idleTimeoutMs) {
     opt_idleTimeoutMs = opt_idleTimeoutMs || 250;
 
-    let loadOnIdle = function() {
+    var loadOnIdle = function() {
       window.requestIdleCallback(function() {
         loadAssets(id, callback);
       }, { timeout: opt_idleTimeoutMs });
     };
 
-    if (document.readyState == 'complete') {
+    if (document.readyState == 'loading') {
+      window.addEventListener('DOMContentLoaded', loadOnIdle);
+    } else {
+      // DOMContentLoaded has already been called if document.readyState is
+      // 'interactive' or 'complete', so invoke the callback immediately.
       loadOnIdle();
-    } else {
-      window.addEventListener('DOMContentLoaded', loadOnIdle);
     }
   }
 
   /**
    * Wait until the element with the given |id| has finished its layout,
    * specifically, after it has an offsetHeight > 0.
    * @param {string} id Identifier of the element to wait for.
    * @param {function()} callback Function to invoke when done loading.
    */
   function waitUntilLayoutComplete(id, callback) {
@@ skipping 12 matching lines @@
 
   return {
     alreadyLoadedAssets: alreadyLoadedAssets,
     hasDeferredAssets: hasDeferredAssets,
     loadAssets: loadAssets,
     loadAssetsOnIdle: loadAssetsOnIdle,
     waitUntilLayoutComplete: waitUntilLayoutComplete,
     registerAssets: registerAssets
   };
 });