Fix login navigation button enabling

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

 // Copyright (c) 2012 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 signin screen implementation.
  */
 
 login.createScreen('GaiaSigninScreen', 'gaia-signin', function() {
   // GAIA animation guard timer. Started when GAIA page is loaded
@@ skipping 500 matching lines @@
 
       // Ensure that GAIA signin (or loading UI) is actually visible.
       window.requestAnimationFrame(function() {
         chrome.send('loginVisible', ['gaia-loading']);
       });
 
       // Button header is always visible when sign in is presented.
       // Header is hidden once GAIA reports on successful sign in.
       Oobe.getInstance().headerHidden = false;
 
+      // Re-enable navigation in case it was disabled before refresh.
+      this.navigation_.disabled = false;
+
       this.lastBackMessageValue_ = false;
       this.updateControlsState();
     },
 
     getSigninFrame_: function() {
       switch (this.screenMode_) {
         case ScreenMode.DEFAULT:
           return $('signin-frame');
         case ScreenMode.OFFLINE:
           return $('offline-gaia');
@@ skipping 533 matching lines @@
 
       if (show)
         $('gaia-whitelist-error').submitButton.focus();
       else
         Oobe.showSigninUI();
 
       this.updateControlsState();
     }
   };
 });