Correctly fire active descendant changes for more roles

chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs

 // 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.
 
 // Include test fixture.
 GEN_INCLUDE(['../../testing/chromevox_next_e2e_test_base.js',
              '../../testing/assert_additions.js']);
 
 GEN_INCLUDE(['../../testing/mock_feedback.js']);
 
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   this.runWithLoadedTree(function(root) {/*!
     <input type="submit" aria-label="foo" value="foo"></input>
   */}, function(root) {
     var btn = root.find({role: RoleType.button});
     mockFeedback.call(btn.focus.bind(btn))
         .expectSpeech('foo')
         .expectSpeech('Button')
         .replay();
   });
 });
+
+TEST_F('BackgroundTest', 'ActiveDescendantOnPopupButton', function() {
+  var mockFeedback = this.createMockFeedback();
+  this.runWithLoadedTree(function(root) {/*!
+    <button id="a" aria-activedescendant="b" aria-haspopup="true">a</button>
+    <p id="b">b</p>
+    <p id="c">c</p>
+    <script>
+      var alt = false;
+      setInterval(function() {
+        var id = alt ? 'b' : 'c';
+        document.getElementById('a').setAttribute('aria-activedescendant', id);
+        alt = !alt;
+      }, 500);
+    </script>
+  */}, function(root) {
+    root.find({role: RoleType.popUpButton}).focus();
+    mockFeedback.expectSpeech('a')
+        .expectSpeech('b')
+        .expectSpeech('Button')
+        .expectSpeech('b')
+        .expectSpeech('c')
+        .expectSpeech('b')
+        .replay();
+  });
+});