Add a test for the "ephemeral_users_enabled" device policy

chrome/test/functional/PYAUTO_TESTS

 # Copyright (c) 2012 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.
 #
 # This file lists the pyauto tests that run as a part of the functional test
 # suite.
 #
 # Tests can be enabled on a per-platform basis. Tests not listed here will
 # not be run.
 #
@@ skipping 650 matching lines @@
   'CHROMEOS_LOGIN': {
     'chromeos': [
       'chromeos_login',
     ],
   },
 
   # ChromeOS policy tests. These are shared with Desktop Chrome tests, but
   # require custom setup on ChromeOS.
   'CHROMEOS_POLICY': {
     'chromeos': [
+      'chromeos_ephemeral',
       'chromeos_onc',
       'policy',
       'policy_prefs_ui',
       # crbug.com/115427
       '-policy.PolicyTest.testAlwaysAuthorizePlugins',
       # crbug.com/118054
       '-policy.PolicyTest.testApplicationLocaleValue',
       # crbug.com/118123
       '-policy.PolicyTest.testExtensionInstallFromForceList',
       '-policy.PolicyTest.testSetDownloadDirectory',
@@ skipping 34 matching lines @@
 
   # HTML5 media performance tests.
   'AV_PERF': {
      'linux': [
        'media.media_constrained_network_perf',
        'media.media_jerky',
        'media.media_stat_perf',
      ],
   },
 }