[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 256 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;
+        extensionList.onExtensionCountChanged =
+            this.updateListVisibility_.bind(this);
+        this.updateListVisibility_();

[Dan Beam, 2015/04/27 16:17:05]

why does the |this| matter at all for this method?

       }.bind(this));
     },
 
     /**
+     * Updates the visibility of the extension list and "Boo..." message.
+     * @private
+     */
+    updateListVisibility_: function() {

[Dan Beam, 2015/04/27 16:17:05]

make this static

[Devlin, 2015/04/27 18:28:30]

Now, since this is a delegate method, I don't think this makes as much sense. 
Lemme know if you still want me to.

[Dan Beam, 2015/04/27 18:47:59]

fine as is

+      /** @const */
+      var hasExtensions = $('extension-settings-list').getNumExtensions() != 0;
+      $('no-extensions').hidden = hasExtensions;
+      $('extension-list-wrapper').hidden = !hasExtensions;
+    },
+
+    /**
      * Handles the Pack Extension button.
      * @param {Event} e Change event.
      * @private
      */
     handlePackExtension_: function(e) {
       ExtensionSettings.showOverlay($('pack-extension-overlay'));
       chrome.send('metricsHandler:recordAction', ['Options_PackExtension']);
     },
 
     /**
@@ skipping 55 matching lines @@
   };
 
   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() {

[Dan Beam, 2015/04/27 16:17:05]

^ this is an example of a static method

     return document.querySelector('#overlay .page.showing');
   };
 
   /**
    * Sets the given overlay to show. If the overlay is already showing, this is
    * a no-op; otherwise, hides any currently-showing overlay.
    * @param {HTMLElement} node The overlay page to show. If null, all overlays
    *     are hidden.
    */
   ExtensionSettings.showOverlay = function(node) {
@@ skipping 87 matching lines @@
   // Export
   return {
     ExtensionSettings: ExtensionSettings
   };
 });
 
 window.addEventListener('load', function(e) {
   document.documentElement.classList.add('loading');
   extensions.ExtensionSettings.getInstance().initialize();
 });