Settings: Fix closing the alert overlay opened from other overlays.

chrome/browser/resources/options2/alert_overlay.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('options', function() {
   var OptionsPage = options.OptionsPage;
 
   /**
    * AlertOverlay class
    * Encapsulated handling of a generic alert.
@@ skipping 26 matching lines @@
       var self = this;
       $('alertOverlayOk').onclick = function(event) {
         self.handleOK_();
       };
 
       $('alertOverlayCancel').onclick = function(event) {
         self.handleCancel_();
       };
     },
 
+    /** @inheritDoc */
+    get nestingLevel() {
+      // AlertOverlay is special in that it is not tied to one page or overlay.
+      // Set the nesting level arbitrarily high so as to always be recognized as
+      // the top-most visible page.
+      return 99;
+    },
+
     /**
      * Handle the 'ok' button.  Clear the overlay and call the ok callback if
      * available.
      * @private
      */
     handleOK_: function() {
       OptionsPage.closeOverlay();
       if (this.okCallback != undefined) {
         this.okCallback.call();
       }
@@ skipping 78 matching lines @@
     // Intentionally don't show the URL in the location bar as we don't want
     // people trying to navigate here by hand.
     OptionsPage.showPageByName('alertOverlay', false);
   };
 
   // Export
   return {
     AlertOverlay: AlertOverlay
   };
 });