Implement ChromeVox Next menus.

chrome/browser/resources/chromeos/chromevox/common/composite_tts.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.
 
 /**
  * @fileoverview A composite TTS sends allows ChromeVox to use
  * multiple TTS engines at the same time.
  *
  */
 
@@ skipping 76 matching lines @@
     function(propertyName, increase) {
   this.ttsEngines_.forEach(function(engine) {
     engine.increaseOrDecreaseProperty(propertyName, increase);
   });
 };
 
 
 /**
  * @override
  */
+cvox.CompositeTts.prototype.propertyToPercentage = function(property) {
+  for (var i = 0, engine; engine = this.ttsEngines_[i]; i++) {
+    var value = engine.propertyToPercentage(property);
+    if (value !== undefined)
+      return value;
+  }
+};
+
+
+/**
+ * @override
+ */
 cvox.CompositeTts.prototype.getDefaultProperty = function(property) {
   for (var i = 0, engine; engine = this.ttsEngines_[i]; i++) {
     var value = engine.getDefaultProperty(property);
-    if (value) {
+    if (value !== undefined)
       return value;
-    }
   }
   return null;
 };