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

chrome/browser/resources/options/about_page.js

Index: chrome/browser/resources/options/about_page.js
diff --git a/chrome/browser/resources/options/about_page.js b/chrome/browser/resources/options/about_page.js
index a6490a3a5db1007ee10e02294a59e931e81ec771..9d2c126e2abdb7aac999ea5d679189cdb1545bbb 100644
--- a/chrome/browser/resources/options/about_page.js
+++ b/chrome/browser/resources/options/about_page.js
@@ -49,6 +49,15 @@ cr.define('options', function() {
     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) {
@@ -67,6 +76,10 @@ cr.define('options', function() {
     $('updateIcon').className= 'update-icon ' + state;
   };
 
+  AboutPage.changeToRestartButton = function() {
+    AboutPage.getInstance().changeToRestartButton_();
+  };
+
   // Export
   return {
     AboutPage: AboutPage