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

chrome/browser/resources/uber/uber.js

Index: chrome/browser/resources/uber/uber.js
diff --git a/chrome/browser/resources/uber/uber.js b/chrome/browser/resources/uber/uber.js
index c46a82137592b2e0859c425b8ff24cd550aa17b9..4157e40ef9dd1b611903fbcdcb132e3f39189fad 100644
--- a/chrome/browser/resources/uber/uber.js
+++ b/chrome/browser/resources/uber/uber.js
@@ -151,6 +151,8 @@ cr.define('uber', function() {
    */
   function backgroundNavigation() {
     navFrame.classList.add('background');
+    navFrame.firstChild.tabIndex = -1;
+    navFrame.firstChild.setAttribute('aria-hidden', true);
   }
 
   /**
@@ -158,6 +160,8 @@ cr.define('uber', function() {
    */
   function foregroundNavigation() {
     navFrame.classList.remove('background');
+    navFrame.firstChild.tabIndex = 0;
+    navFrame.firstChild.removeAttribute('aria-hidden');
   }
 
   /**