[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;
-        $('extension-settings-list').updateFocusableElements();
+        var onHasExtensionsChanged = function() {

[Dan Beam, 2015/04/23 18:01:39]

onExtensionChanged (or at the very least HaveExtensions or HasExtension, right
now this makes little sense...)

[Devlin, 2015/04/23 18:27:31]

How about onExtensionCountChanged?  (Before, it was saying that the property
'hasExtensions' on the list has changed, not that the extensions themselves have
changed.  But yes, it was very weirdly phrased.)

+          /** @const */
+          var hasExtensions = extensionList.getNumExtensions() != 0;
+          $('no-extensions').hidden = hasExtensions;
+          $('extension-list-wrapper').hidden = !hasExtensions;
+          $('extension-settings-list').updateFocusableElements();
+        };

[Dan Beam, 2015/04/23 18:01:38]

make this a permanent instance or static method instead of this weird dance
you're doing

[Devlin, 2015/04/23 18:27:31]

Done.

+        extensionList.onHasExtensionsChanged = onHasExtensionsChanged;
+        onHasExtensionsChanged();
       }.bind(this));
     },
 
     /**
      * Handles the Pack Extension button.
      * @param {Event} e Change event.
      * @private
      */
     handlePackExtension_: function(e) {
       ExtensionSettings.showOverlay($('pack-extension-overlay'));
@@ skipping 167 matching lines @@
   // Export
   return {
     ExtensionSettings: ExtensionSettings
   };
 });
 
 window.addEventListener('load', function(e) {
   document.documentElement.classList.add('loading');
   extensions.ExtensionSettings.getInstance().initialize();
 });