WebUI: Return focus to anchor element when cr-action-menu is closed.

chrome/test/data/webui/cr_elements/cr_action_menu_test.js

 // Copyright 2016 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 Tests for cr-action-menu element. */
 suite('CrActionMenu', function() {
   /** @type {?CrActionMenuElement} */
   var menu = null;
 
   /** @type {?NodeList<HTMLElement>} */
@@ skipping 75 matching lines @@
   });
 
   test('close on resize', function() {
     menu.showAt(document.querySelector('#dots'));
     assertTrue(menu.open);
 
     window.dispatchEvent(new CustomEvent('resize'));
     assertFalse(menu.open);
   });
 
-  test('close on Tab', function() {
-    menu.showAt(document.querySelector('#dots'));
-    assertTrue(menu.open);
+  /** @param {string} key The key to use for closing. */
+  function testFocusAfterClosing(key) {
+    return new Promise(function(resolve) {
+      var dots = document.querySelector('#dots');
+      menu.showAt(dots);
+      assertTrue(menu.open);
 
-    MockInteractions.keyDownOn(menu, 'Tab', [], 'Tab');
-    assertFalse(menu.open);
+      // Check that focus returns to the anchor element.
+      dots.addEventListener('focus', resolve);
+      MockInteractions.keyDownOn(menu, key, [], key);
+      assertFalse(menu.open);
+    });
+  }
+
+  test('close on Tab', function() { return testFocusAfterClosing('Tab'); });
+  test('close on Escape', function() {
+    return testFocusAfterClosing('Escape');
   });
 });