Typecheck JS files for chrome://extensions

chrome/browser/resources/extensions/extension_options_overlay.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.
 
 cr.define('extensions', function() {
   'use strict';
 
   /**
    * The ExtensionOptionsOverlay will show an extension's options page using
    * an <extensionoptions> element.
    * @constructor
    */
   function ExtensionOptionsOverlay() {}
 
   cr.addSingletonGetter(ExtensionOptionsOverlay);
 
   ExtensionOptionsOverlay.prototype = {
     /**
      * The function that shows the given element in the overlay.
-     * @type {Function}
-     * @param {HTMLElement} The element to show in the overlay.
+     * @type {?function(HTMLDivElement)} Function that receives the element to
+     *     show in the overlay.
      * @private
      */
-    showOverlay_: undefined,
+    showOverlay_: null,
 
     /**
      * Initialize the page.
      * @param {function(HTMLDivElement)} showOverlay The function to show or
      *     hide the ExtensionOptionsOverlay; this should take a single parameter
      *     which is either the overlay Div if the overlay should be displayed,
      *     or null if the overlay should be hidden.
      */
     initializePage: function(showOverlay) {
       var overlay = $('overlay');
 
       cr.ui.overlay.setupOverlay(overlay);
       cr.ui.overlay.globalInitialization();
       overlay.addEventListener('cancelOverlay', this.handleDismiss_.bind(this));
 
       this.showOverlay_ = showOverlay;
     },
 
     /**
      * Handles a click on the close button.
-     * @param {Event} e The click event.
+     * @param {Event} event The click event.
      * @private
      */
     handleDismiss_: function(event) {
       this.setVisible_(false);
       var extensionoptions = document.querySelector('extensionoptions');
       if (extensionoptions)
         $('extension-options-overlay').removeChild(extensionoptions);
     },
 
     /**
@@ skipping 20 matching lines @@
 
       this.setVisible_(true);
     },
 
     /**
      * Toggles the visibility of the ExtensionOptionsOverlay.
      * @param {boolean} isVisible Whether the overlay should be visible.
      * @private
      */
     setVisible_: function(isVisible) {
-      this.showOverlay_(isVisible ? $('extension-options-overlay') : null);
+      this.showOverlay_(isVisible ?
+          /** @type {HTMLDivElement} */($('extension-options-overlay')) :
+          null);
     }
   };
 
   // Export
   return {
     ExtensionOptionsOverlay: ExtensionOptionsOverlay
   };
 });