Fix flaky NPE in oobe.js.

chrome/browser/resources/chromeos/login/login_shared.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.
 
 /**
  * @fileoverview Common OOBE controller methods. This method is shared between
  * OOBE, login, and the lock screen. Add only methods that need to be shared
  * between all *three* screens here, as each additional method increases the
  * time it takes to show the lock screen.
  *
@@ skipping 32 matching lines @@
    * Delay in milliseconds between start of OOBE animation and start of
    * header bar animation.
    */
   var HEADER_BAR_DELAY_MS = 300;
 
   cr.addSingletonGetter(Oobe);
 
   Oobe.prototype = {
     __proto__: DisplayManager.prototype,
   };
 

[Shuhei Takahashi, 2017/04/07 04:37:59]

Could you define Oobe.readyForTesting here with JSDoc?

[hidehiko, 2017/04/07 06:37:59]

Done.

   /**
    * Handle accelerators. These are passed from native code instead of a JS
    * event handler in order to make sure that embedded iframes cannot swallow
    * them.
    * @param {string} name Accelerator name.
    */
   Oobe.handleAccelerator = function(name) {
     Oobe.getInstance().handleAccelerator(name);
   };
 
@@ skipping 369 matching lines @@
          src instanceof HTMLInputElement &&
          /text|password|search/.test(src.type);
 });
 
 
 (function() {
   'use strict';
 
   document.addEventListener('DOMContentLoaded', function() {
     Oobe.initialize();
+
+    // Some ForTesting APIs directly access to DOM. Because this script
+    // is loaded in header, DOM tree may not be available at beginning.
+    // initialize() is called on DOMContentLoaded, so here mark ready,
+    // and let the external script wait for this condition.
+    Oobe.readyForTesting = true;
   });
 
   // Install a global error handler so stack traces are included in logs.
   window.onerror = function(message, file, line, column, error) {
     console.error(error.stack);
   }
 })();
-