Mark supervised profiles as such immediately when they're created.

chrome/browser/ui/webui/downloads_ui_browsertest.js

 // Copyright 2013 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.
 
 GEN('#include "chrome/browser/ui/webui/downloads_ui_browsertest.h"');
 
 /** @const */ var TOTAL_RESULT_COUNT = 25;
 
 /**
  * Test C++ fixture for downloads WebUI testing.
@@ skipping 153 matching lines @@
  * Fixture for Downloads WebUI testing for a supervised user.
  * @extends {BaseDownloadsWebUITest}
  * @constructor
  */
 function DownloadsWebUIForSupervisedUsersTest() {}
 
 DownloadsWebUIForSupervisedUsersTest.prototype = {
   __proto__: BaseDownloadsWebUITest.prototype,
 
   /** @override */
-  testGenPreamble: function() {
-    GEN('  ChangeProfileToSupervised();');
-  },
+  typedefCppFixture: 'DownloadsWebUIForSupervisedUsersTest',
 };
 
 // Test UI for supervised users, removing entries should be disabled
 // and removal controls should be hidden.
 TEST_F('DownloadsWebUIForSupervisedUsersTest', 'SupervisedUsers', function() {
   this.testHelper(false, true);
   testDone();
 });