Revert of Revert "Typecheck JS files for chrome://extensions"

chrome/browser/resources/extensions/extension_options_overlay.js

Index: chrome/browser/resources/extensions/extension_options_overlay.js
diff --git a/chrome/browser/resources/extensions/extension_options_overlay.js b/chrome/browser/resources/extensions/extension_options_overlay.js
index e51e1fe34b664cb5b620fe0f09dc006ede6ca026..2f16eb60c96c78a7152dd24a83b14bc22b4bcd39 100644
--- a/chrome/browser/resources/extensions/extension_options_overlay.js
+++ b/chrome/browser/resources/extensions/extension_options_overlay.js
@@ -17,11 +17,11 @@
   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.
@@ -42,7 +42,7 @@
 
     /**
      * Handles a click on the close button.
-     * @param {Event} e The click event.
+     * @param {Event} event The click event.
      * @private
      */
     handleDismiss_: function(event) {
@@ -150,7 +150,9 @@
      * @private
      */
     setVisible_: function(isVisible) {
-      this.showOverlay_(isVisible ? $('extension-options-overlay') : null);
+      this.showOverlay_(isVisible ?
+          /** @type {HTMLDivElement} */($('extension-options-overlay')) :
+          null);
     }
   };