Set default control on Terms of Service screen

chrome/browser/resources/chromeos/login/oobe_screen_terms_of_service.js

 // Copyright (c) 2013 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 Oobe Terms of Service screen implementation.
  */
 
 cr.define('oobe', function() {
   /**
@@ skipping 19 matching lines @@
    */
   TermsOfServiceScreen.setDomain = function(domain) {
     $('tos-heading').textContent =
         localStrings.getStringF('termsOfServiceScreenHeading', domain);
     $('tos-subheading').textContent =
         localStrings.getStringF('termsOfServiceScreenSubheading', domain);
     $('tos-content-heading').textContent =
         localStrings.getStringF('termsOfServiceContentHeading', domain);
   };
 
+  /**
+   * Displays the given |termsOfService|, enables the accept button and moves
+   * the focus to it.
+   * @param {string} termsOfService The terms of service, as plain text.
+   */
+  TermsOfServiceScreen.setTermsOfService = function(termsOfService) {
+    $('terms-of-service').classList.remove('tos-loading');
+    $('tos-content-main').textContent = termsOfService;
+    $('tos-accept-button').disabled = false;
+    // Initially, the back button is focused and the accept button is disabled.
+    // Move the focus to the accept button now but only if the user has not
+    // moved the focus anywhere in the meantime.
+    if (!$('tos-back-button').blurred)

[Nikita (slow), 2013/02/12 20:51:48]

nit: You could check what's the current document.activeElement is so that you
won't need additional property (blurred).

[bartfab (slow), 2013/02/12 23:22:59]

The property actually is needed to achieve the semantics I am after: I want to
avoid changing the focus if the user has modified the focus manually in any way,
even if that included moving the focus back to the button that was focused
initially. So I do not want to find out whether the default button is focused
right now, I want to find out whether it had ever lost focus in the past.

+      $('tos-accept-button').focus();
+  };
+
   TermsOfServiceScreen.prototype = {
     // Set up the prototype chain.
     __proto__: HTMLDivElement.prototype,
 
     /** @override */
     decorate: function() {
     },
 
     /**
      * Buttons in Oobe wizard's button strip.
      * @type {array} Array of Buttons.
      */
     get buttons() {
       var buttons = [];
 
       var backButton = this.ownerDocument.createElement('button');
       backButton.id = 'tos-back-button';
       backButton.textContent =
           localStrings.getString('termsOfServiceBackButton');
       backButton.addEventListener('click', function(event) {
         $('tos-back-button').disabled = true;
         $('tos-accept-button').disabled = true;
         chrome.send('termsOfServiceBack');
       });
+      backButton.addEventListener('blur', function(event) {
+        this.blurred = true;
+      });
       buttons.push(backButton);
 
       var acceptButton = this.ownerDocument.createElement('button');
       acceptButton.id = 'tos-accept-button';
       acceptButton.disabled = true;
       acceptButton.classList.add('preserve-disabled-state');
       acceptButton.textContent =
           localStrings.getString('termsOfServiceAcceptButton');
       acceptButton.addEventListener('click', function(event) {
         $('tos-back-button').disabled = true;
         $('tos-accept-button').disabled = true;
         chrome.send('termsOfServiceAccept');
       });
       buttons.push(acceptButton);
 
       return buttons;
     },
 
     /**
+     * Returns the control which should receive initial focus.
+     */
+    get defaultControl() {
+      return $('tos-accept-button').disabled ? $('tos-back-button') :
+                                               $('tos-accept-button');
+    },
+
+    /**
      * Event handler that is invoked just before the screen is shown.
      * @param {object} data Screen init payload.
      */
     onBeforeShow: function(data) {
       Oobe.getInstance().headerHidden = true;
     },
   };
 
   return {
     TermsOfServiceScreen: TermsOfServiceScreen
   };
 });