Refactor event handler classes to make it easier to add new event type listeners.

chrome/browser/resources/chromeos/chromevox/chromevox/background/background.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 Script that runs on the background page.
  */
 
 goog.provide('cvox.ChromeVoxBackground');
 
@@ skipping 142 matching lines @@
 
   this.tabsApiHandler_ = new cvox.TabsApiHandler();
 
   // Export globals on cvox.ChromeVox.
   cvox.ChromeVox.tts = this.tts;
   cvox.ChromeVox.braille = this.backgroundBraille_;
 
   if (!cvox.ChromeVox.earcons)
     cvox.ChromeVox.earcons = new cvox.ClassicEarcons();
 
-  if (cvox.ChromeVox.isChromeOS &&
-      chrome.accessibilityPrivate.onIntroduceChromeVox) {
+  if (cvox.ChromeVox.isChromeOS) {
     chrome.accessibilityPrivate.onIntroduceChromeVox.addListener(
         this.onIntroduceChromeVox);
   }
 
   // Set up a message passing system for goog.provide() calls from
   // within the content scripts.
   chrome.extension.onMessage.addListener(
       function(request, sender, callback) {
         if (request['srcFile']) {
           var srcFile = request['srcFile'];
@@ skipping 317 matching lines @@
   window['braille_translator_manager'] =
       background.backgroundBraille_.getTranslatorManager();
 
   window['getCurrentVoice'] =
       background.getCurrentVoice.bind(background);
 
   // Export injection for ChromeVox Next.
   cvox.ChromeVox.injectChromeVoxIntoTabs =
       background.injectChromeVoxIntoTabs.bind(background);
 })();