[Extensions Page] Add a listener on extension list for "hasExtensions" changing

chrome/browser/resources/extensions/extensions.js

 // Copyright (c) 2012 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 src="../../../../ui/webui/resources/js/cr/ui/focus_row.js">
 <include src="../../../../ui/webui/resources/js/cr/ui/focus_grid.js">
 <include src="../uber/uber_utils.js">
 <include src="extension_code.js">
 <include src="extension_commands_overlay.js">
 <include src="extension_error_overlay.js">
@@ skipping 80 matching lines @@
     hideDropTargetOverlay_: function() {
       var currentOverlay = ExtensionSettings.getCurrentOverlay();
       if (currentOverlay && currentOverlay.id === 'drop-target-overlay')
         ExtensionSettings.showOverlay(null);
     }
   };
 
   /**
    * ExtensionSettings class
    * @class
+   * @constructor
+   * @implements {ExtensionList.Delegate}
    */
   function ExtensionSettings() {}
 
   cr.addSingletonGetter(ExtensionSettings);
 
   ExtensionSettings.prototype = {
     __proto__: HTMLDivElement.prototype,
 
     /**
      * The drag-drop wrapper for installing external Extensions, if available.
@@ skipping 15 matching lines @@
      * Perform initial setup.
      */
     initialize: function() {
       uber.onContentFrameLoaded();
       cr.ui.FocusOutlineManager.forDocument(document);
       measureCheckboxStrings();
 
       // Set the title.
       uber.setTitle(loadTimeData.getString('extensionSettings'));
 
-      var extensionList = new ExtensionList();
+      var extensionList = new ExtensionList(this);
       extensionList.id = 'extension-settings-list';
       var wrapper = $('extension-list-wrapper');
       wrapper.insertBefore(extensionList, wrapper.firstChild);
 
       this.update_();
       // TODO(devlin): Remove this once all notifications are moved to events on
       // the developerPrivate api.
       chrome.send('extensionSettingsRegister');
 
       var extensionLoader = extensions.ExtensionLoader.getInstance();
@@ skipping 120 matching lines @@
           profileInfo.appInfoDialogEnabled).then(function() {
         // We can get called many times in short order, thus we need to
         // be careful to remove the 'finished loading' timeout.
         if (this.loadingTimeout_)
           window.clearTimeout(this.loadingTimeout_);
         document.documentElement.classList.add('loading');
         this.loadingTimeout_ = window.setTimeout(function() {
           document.documentElement.classList.remove('loading');
         }, 0);
 
-        /** @const */
-        var hasExtensions = extensionList.getNumExtensions() != 0;
-        $('no-extensions').hidden = hasExtensions;
-        $('extension-list-wrapper').hidden = !hasExtensions;
+        this.onExtensionCountChanged();
       }.bind(this));
     },
 
     /**
      * Handles the Pack Extension button.
      * @param {Event} e Change event.
      * @private
      */
     handlePackExtension_: function(e) {
       ExtensionSettings.showOverlay($('pack-extension-overlay'));
       chrome.send('metricsHandler:recordAction', ['Options_PackExtension']);
     },
 
     /**
      * Shows the Extension Commands configuration UI.
-     * @param {Event} e Change event.
      * @private
      */
-    showExtensionCommandsConfigUi_: function(e) {
+    showExtensionCommandsConfigUi_: function() {
       ExtensionSettings.showOverlay($('extension-commands-overlay'));
       chrome.send('metricsHandler:recordAction',
                   ['Options_ExtensionCommands']);
     },
 
     /**
      * Handles the Configure (Extension) Commands link.
      * @param {Event} e Change event.
      * @private
      */
@@ skipping 30 matching lines @@
                                    function(control) {
         control.tabIndex = showDevControls ? 0 : -1;
       });
       buttons.setAttribute('aria-hidden', !showDevControls);
 
       window.requestAnimationFrame(function() {
         devControls.style.height = !showDevControls ? '' :
             buttons.offsetHeight + 'px';
       }.bind(this));
     },
+
+    /** @override */
+    onExtensionCountChanged: function() {
+      /** @const */
+      var hasExtensions = $('extension-settings-list').getNumExtensions() != 0;
+      $('no-extensions').hidden = hasExtensions;
+      $('extension-list-wrapper').hidden = !hasExtensions;
+    },
   };
 
+  /**
+   * Called by the WebUI when something has changed and the extensions UI needs
+   * to be updated.
+   */
   ExtensionSettings.onExtensionsChanged = function() {
     ExtensionSettings.getInstance().update_();
   };
 
   /**
    * Returns the current overlay or null if one does not exist.
    * @return {Element} The overlay element.
    */
   ExtensionSettings.getCurrentOverlay = function() {
     return document.querySelector('#overlay .page.showing');
@@ skipping 96 matching lines @@
   // Export
   return {
     ExtensionSettings: ExtensionSettings
   };
 });
 
 window.addEventListener('load', function(e) {
   document.documentElement.classList.add('loading');
   extensions.ExtensionSettings.getInstance().initialize();
 });