Show "Update Chrome OS" in the wrench menu, when the update image is ready.

chrome/browser/resources/options/about_page.js

 // Copyright (c) 2010 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.
 
 cr.define('options', function() {
   const OptionsPage = options.OptionsPage;
 
   /**
    * Encapsulated handling of about page.
    */
@@ skipping 31 matching lines @@
       $('osVersion1').textContent = versionString;
     },
 
     updateStatus_: function(message) {
       $('updateStatus').textContent = message;
     },
 
     updateEnable_: function(enable) {
       $('checkNow').disabled = !enable;
     },
+
+    // Changes the "check now" button to "restart now" button.
+    changeToRestartButton_: function() {
+      $('checkNow').textContent = localStrings.getString('restart_now');
+      $('checkNow').disabled = false;
+      $('checkNow').onclick = function(event) {
+        chrome.send('RestartNow');
+      };
+    },
   };
 
   AboutPage.updateOSVersionCallback = function(versionString) {
     AboutPage.getInstance().updateOSVersion_(versionString);
   };
 
   AboutPage.updateStatusCallback = function(message) {
     AboutPage.getInstance().updateStatus_(message);
   };
 
   AboutPage.updateEnableCallback = function(enable) {
     AboutPage.getInstance().updateEnable_(enable);
   };
 
   AboutPage.setUpdateImage = function(state) {
     $('updateIcon').className= 'update-icon ' + state;
   };
 
+  AboutPage.changeToRestartButton = function() {
+    AboutPage.getInstance().changeToRestartButton_();
+  };
+
   // Export
   return {
     AboutPage: AboutPage
   };
 
 });