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

chrome/browser/resources/chromeos/chromevox/chromevox/background/tabs_api_handler.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 Accesses Chrome's tabs extension API and gives
  * feedback for events that happen in the "Chrome of Chrome".
  */
 
 goog.provide('cvox.TabsApiHandler');
@@ skipping 181 matching lines @@
    * Installs a new automation handler for the given tab.
    * @param {number} tabId
    * @private
    */
   refreshAutomationHandler_: function(tabId) {
     if (!cvox.ChromeVox.isMac)
       return;
 
     chrome.automation.getTree(tabId, function(node) {
       if (this.handler_)
-        this.handler_.unregister();
+        this.handler_.removeAllListeners();
 
       this.handler_ = new TabsAutomationHandler(node);
     }.bind(this));
   },
 
   /**
    * @param {number} id Tab id to focus.
    * @private
    */
   focusTab_: function(id) {
@@ skipping 38 matching lines @@
   },
 
   /**
    * @return {boolean} True if the page loading sound is playing and our
    * page loading timer is active.
    */
   isPlayingPageLoadingSound_: function() {
     return this.pageLoadIntervalID_ != null;
   }
 };