Typecheck JS files for chrome://extensions

chrome/browser/resources/extensions/extension_error.js

Index: chrome/browser/resources/extensions/extension_error.js
diff --git a/chrome/browser/resources/extensions/extension_error.js b/chrome/browser/resources/extensions/extension_error.js
index 28f3dc4832e1cf1741fa9b74bb130542efb1c31a..4c5b242f76f869be53a0eb404aac6841f3033b4d 100644
--- a/chrome/browser/resources/extensions/extension_error.js
+++ b/chrome/browser/resources/extensions/extension_error.js
@@ -13,8 +13,8 @@ cr.define('extensions', function() {
    * @return {HTMLElement} The clone of the template.
    */
   function cloneTemplate(templateName) {
-    return $('template-collection-extension-error').
-        querySelector('.' + templateName).cloneNode(true);
+    return /** @type {HTMLElement} */($('template-collection-extension-error').
+        querySelector('.' + templateName).cloneNode(true));
   }
 
   /**
@@ -44,7 +44,10 @@ cr.define('extensions', function() {
   ExtensionError.prototype = {
     __proto__: HTMLDivElement.prototype,
 
-    /** @override */
+    /**
+     * @param {BackendExtensionErrorObject} error
+     * @override
+     */
     decorate: function(error) {
       // Add an additional class for the severity level.
       if (error.level == 0)