Introduce concept of provisional destinations to print preview

chrome/browser/resources/print_preview/print_preview_focus_manager.js

 // Copyright 2014 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('print_preview', function() {
   'use strict';
 
   /**
    * FocusManager implementation specialized for Print Preview, which ensures
    * that Print Preview itself does not receive focus when an overlay is shown.
    * @constructor
    * @extends {cr.ui.FocusManager}
    */
   function PrintPreviewFocusManager() {
   };
 
   cr.addSingletonGetter(PrintPreviewFocusManager);
 
   PrintPreviewFocusManager.prototype = {
     __proto__: cr.ui.FocusManager.prototype,
 
     /** @override */
     getFocusParent: function() {
-      return document.querySelector('.overlay:not([hidden])') ||
-          document.body;
+      var el = document.body;

[tbarzic, 2015/05/27 17:10:11]

needed to handle showing an overlay (USB permission warning dialog) on top of
another overlay (destination search UI).

+      var newEl = null;
+      while (newEl = el.querySelector('.overlay:not([hidden])'))
+        el = newEl;
+      return el;
     }
   };
 
   // Export
   return {
     PrintPreviewFocusManager: PrintPreviewFocusManager
   };
 });