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

chrome/browser/resources/md_extensions/load_error.js

 // Copyright 2017 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';
 
   /** @interface */
   function LoadErrorDelegate() {}
 
   LoadErrorDelegate.prototype = {
     /** Attempts to load the previously-attempted unpacked extension. */
     retryLoadUnpacked: assertNotReached,
   };
 
   var LoadError = Polymer({
     is: 'extensions-load-error',
     properties: {
       /** @type {extensions.LoadErrorDelegate} */
       delegate: Object,
 
-      error: String,
+      /** @type {chrome.developerPrivate.LoadError} */
+      loadError: Object,
+    },
 
-      filePath: String,
-    },
+    observers: [
+      'observeLoadErrorChanges_(loadError)',
+    ],
 
     show: function() {
       this.$$('dialog').showModal();
     },
 
     close: function() {
       this.$$('dialog').close();
     },
 
     /** @private */
     onRetryTap_: function() {
       this.delegate.retryLoadUnpacked();
       this.close();
     },
+
+    /** @private */
+    observeLoadErrorChanges_: function() {
+      assert(this.loadError);
+      var source = this.loadError.source;
+      // CodeSection expects a RequestFileSourceResponse, rather than an
+      // ErrorFileSource. Massage into place.
+      // TODO(devlin): Make RequestFileSourceResponse use ErrorFileSource.
+      var codeSectionProperties = {

[michaelpg, 2017/03/24 02:59:01]

does closure let you "cast" this to @type !RequestFileSourceResponse? (so it can
yell at us if we massage this incorrectly)

[Devlin, 2017/03/24 16:03:08]

Yep, done.

+        beforeHighlight: source ? source.beforeHighlight : '',
+        highlight: source ? source.highlight : '',
+        afterHighlight: source ? source.afterHighlight : '',
+        title: '',
+        message: this.loadError.error,
+      };
+
+      this.$.code.set('code', codeSectionProperties);
+    },
   });
 
   return {LoadError: LoadError,
           LoadErrorDelegate: LoadErrorDelegate};
 });