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

chrome/browser/resources/extensions/extension_code.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.
 
+/**
+ * @typedef {{afterHighlight: string,
+ *            beforeHighlight: string,
+ *            highlight: string,
+ *            title: string}}
+ */
+var ExtensionHighlight;
+
 cr.define('extensions', function() {
   'use strict';
 
   /**
    * ExtensionCode is an element which displays code in a styled div, and is
    * designed to highlight errors.
+   * @constructor
+   * @extends {HTMLDivElement}
    */
   function ExtensionCode(div) {
     div.__proto__ = ExtensionCode.prototype;
     return div;
   }
 
   ExtensionCode.prototype = {
     __proto__: HTMLDivElement.prototype,
 
     /**
      * Populate the content area of the code div with the given code. This will
      * highlight the erroneous section (if any).
-     * @param {Object} code An object with four strings: beforeHighlight,
-     *     afterHighlight, highlight, and the message. The 'highlight' strings
-     *     represent the three portions of the file's content to display - the
-     *     portion which is most relevant and should be emphasized (highlight),
-     *     and the parts both before and after this portion. The message is the
-     *     error message, which will be the mouseover hint for the highlighted
-     *     region. These may be empty.
+     * @param {ExtensionHighlight} code The 'highlight' strings represent the
+     *     three portions of the file's content to display - the portion which
+     *     is most relevant and should be emphasized (highlight), and the parts
+     *     both before and after this portion. The title is the error message,
+     *     which will be the mouseover hint for the highlighted region. These
+     *     may be empty.
      *  @param {string} emptyMessage The message to display if the code
      *     object is empty (e.g., 'could not load code').
      */
     populate: function(code, emptyMessage) {
       // Clear any remnant content, so we don't have multiple code listed.
       this.clear();
 
       var sourceDiv = document.createElement('div');
       sourceDiv.classList.add('extension-code-source');
       this.appendChild(sourceDiv);
@@ skipping 60 matching lines @@
       if (errorSpan)
         this.scrollTop = errorSpan.offsetTop - this.clientHeight / 2;
     }
   };
 
   // Export
   return {
     ExtensionCode: ExtensionCode
   };
 });