[Media Router WebUI] Handle on dialog load focus on Mac.

chrome/test/data/webui/media_router/media_router_elements_browsertest.js

 // Copyright 2015 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 Runs the Media Router Polymer elements tests. */
 
 /** @const {string} Path to source root. */
 var ROOT_PATH = '../../../../../';
 
 // Polymer BrowserTest fixture.
@@ skipping 55 matching lines @@
 
     var requiredOwnedAriaRoleMissingSelectors = [
       '#cast-mode-list',
       '#sink-list'
     ];
 
     // Enable when failure is resolved.
     // AX_ARIA_08: http://crbug.com/591552
     this.accessibilityAuditConfig.ignoreSelectors(
         'requiredOwnedAriaRoleMissing', requiredOwnedAriaRoleMissingSelectors);
+
+    // This element is used as a focus placeholder on dialog open, then
+    // deleted. The user will be unable to tab to it. Remove when there is a
+    // long term fix.
+    this.accessibilityAuditConfig.ignoreSelectors(
+       'focusableElementNotVisibleAndNotAriaHidden', '#focus-placeholder');
   },
 };
 
 TEST_F('MediaRouterElementsBrowserTest', 'IssueBanner', function() {
   issue_banner.registerTests();
   mocha.run();
 });
 
 // The media-router-container tests are being split into multiple parts due to
 // timeout issues on bots.
@@ skipping 41 matching lines @@
     'MediaRouterSearchHighlighter',
     function() {
   media_router_search_highlighter.registerTests();
   mocha.run();
 });
 
 TEST_F('MediaRouterElementsBrowserTest', 'MediaRouterRouteDetails', function() {
   route_details.registerTests();
   mocha.run();
 });