Use children changed events to monitor active descendant changes.

chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.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 Handles automation from a desktop automation node.
  */
 
 goog.provide('DesktopAutomationHandler');
 
@@ skipping 29 matching lines @@
    * @type {!Date}
    * @private
    */
   this.lastValueChanged_ = new Date(0);
 
   var e = EventType;
   this.addListener_(e.activedescendantchanged, this.onActiveDescendantChanged);
   this.addListener_(e.alert, this.onAlert);
   this.addListener_(e.ariaAttributeChanged, this.onEventIfInRange);
   this.addListener_(e.checkedStateChanged, this.onCheckedStateChanged);
+  this.addListener_(e.childrenChanged, this.onActiveDescendantChanged);
   this.addListener_(e.focus, this.onFocus);
   this.addListener_(e.hover, this.onHover);
   this.addListener_(e.loadComplete, this.onLoadComplete);
   this.addListener_(e.menuEnd, this.onMenuEnd);
   this.addListener_(e.menuListItemSelected, this.onEventIfSelected);
   this.addListener_(e.menuStart, this.onMenuStart);
   this.addListener_(e.scrollPositionChanged, this.onScrollPositionChanged);
   this.addListener_(e.selection, this.onSelection);
   this.addListener_(e.textChanged, this.onTextChanged);
   this.addListener_(e.textSelectionChanged, this.onTextSelectionChanged);
@@ skipping 111 matching lines @@
       return;
     Output.flushNextSpeechUtterance();
     this.onEventDefault(evt);
   },
 
   /**
    * Makes an announcement without changing focus.
    * @param {!AutomationEvent} evt
    */
   onActiveDescendantChanged: function(evt) {
-    if (!evt.target.activeDescendant)
+    if (!evt.target.activeDescendant || !evt.target.state.focused)
       return;
     this.onEventDefault(new chrome.automation.AutomationEvent(
         EventType.focus, evt.target.activeDescendant));
   },
 
   /**
    * Makes an announcement without changing focus.
    * @param {!AutomationEvent} evt
    */
   onAlert: function(evt) {
@@ skipping 257 matching lines @@
 DesktopAutomationHandler.init_ = function() {
   chrome.automation.getDesktop(function(desktop) {
     ChromeVoxState.desktopAutomationHandler =
         new DesktopAutomationHandler(desktop);
   });
 };
 
 DesktopAutomationHandler.init_();
 
 });  // goog.scope