Disables the ability to tab to navigation items when an overlay is displayed.

chrome/browser/resources/uber/uber.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.
 
 cr.define('uber', function() {
   var localStrings = new LocalStrings();
 
   /**
    * Options for how web history should be handled.
    */
@@ skipping 133 matching lines @@
       forwardMouseWheel(e.data.params);
     else
       console.error('Received unexpected message', e.data);
   }
 
   /**
    * Sends the navigation iframe to the background.
    */
   function backgroundNavigation() {
     navFrame.classList.add('background');
+    navFrame.firstChild.tabIndex = -1;
+    navFrame.firstChild.setAttribute('aria-hidden', true);
   }
 
   /**
    * Retrieves the navigation iframe from the background.
    */
   function foregroundNavigation() {
     navFrame.classList.remove('background');
+    navFrame.firstChild.tabIndex = 0;
+    navFrame.firstChild.removeAttribute('aria-hidden');
   }
 
   /**
    * Enables or disables animated transitions when changing content while
    * horizontally scrolled.
    * @param {boolean} enabled True if enabled, else false to disable.
    */
   function setContentChanging(enabled) {
     navFrame.classList[enabled ? 'add' : 'remove']('changing-content');
 
@@ skipping 160 matching lines @@
   }
 
   return {
     onLoad: onLoad,
     onPopHistoryState: onPopHistoryState
   };
 });
 
 window.addEventListener('popstate', uber.onPopHistoryState);
 document.addEventListener('DOMContentLoaded', uber.onLoad);