[MD Extensions] Include the manifest code snippet in load errors

chrome/browser/resources/md_extensions/code_section.js

 // Copyright 2016 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';
 
   var CodeSection = Polymer({
     is: 'extensions-code-section',
 
     properties: {
       /**
        * The code this object is displaying.
        * @type {?chrome.developerPrivate.RequestFileSourceResponse}
        */
       code: {
         type: Object,
         // We initialize to null so that Polymer sees it as defined and calls
         // isMainHidden_().
         value: null,
       },
 
       /**
-       * The string to display if no code is set.
+       * The string to display if no |code| is set (e.g. because we couldn't
+       * load the relevant source file).
        * @type {string}
        */
-      noCodeError: String,
+      couldNotDisplayCode: String,
     },
 
     /**
+     * Returns true if no code could be displayed (e.g. because the file could
+     * not be loaded).
+     * @return {boolean}
+     */
+    isEmpty: function() {
+      return !this.code ||
+             (!this.code.beforeHighlight && !this.code.highlight &&
+              !this.code.afterHighlight);
+    },
+
+    /**
      * Computes the content of the line numbers span, which basically just
      * contains 1\n2\n3\n... for the number of lines.
      * @return {string}
      * @private
      */
     computeLineNumbersContent_: function() {
       if (!this.code)
         return '';
 
       var lines = [this.code.beforeHighlight,
                    this.code.highlight,
                    this.code.afterHighlight].join('').match(/\n/g);
       var lineCount = lines ? lines.length : 0;
       var textContent = '';
       for (var i = 1; i <= lineCount; ++i)
         textContent += i + '\n';
       return textContent;
     },
-
-    /**
-     * @return {boolean}
-     * @private
-     */
-    isMainHidden_: function() {
-      return !this.code;
-    },
   });
 
   return {CodeSection: CodeSection};
 });