Prevent parallelization of ash browsertests on the same machine.

scripts/master/factory/chromium_factory.py

 # 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.
 
 """Utility class to build the chromium master BuildFactory's.
 
 Based on gclient_factory.py and adds chromium-specific steps."""
 
 import re
 
@@ skipping 519 matching lines @@
     if R('chromedriver_tests'):
       f.AddGTestTestStep('chromedriver_tests', fp)
     if R('chromedriver_tests_br'):
       f.AddBuildrunnerGTest('chromedriver_tests', fp)
     if R('content_browsertests'):
       f.AddGTestTestStep('content_browsertests', fp)
     if R('content_browsertests_br'):
       f.AddBuildrunnerGTest('content_browsertests', fp)
     if R('ash_browsertests'):
       ash_fp = fp.copy()
-      ash_fp['browser_tests_extra_options'] = ['--ash-browsertests']
+      # Ash browser tests use the Metro environment and thus cannot be ran in
+      # parallel on the same machine.
+      ash_fp['browser_tests_extra_options'] = ['--ash-browsertests',
+                                               '--test-launcher-jobs=1']
       f.AddBuildrunnerBrowserTests(ash_fp)
 
     # Big, UI tests:
     if R('dom_checker'):
       f.AddDomCheckerTests()
     if R('dom_checker_br'):
       f.AddBuildrunnerDomCheckerTests()
 
     if self._target_platform == 'win32':
       if R('installer_util_unittests'):
@@ skipping 819 matching lines @@
                             mode=None, slave_type='BuilderTester', options=None,
                             compile_timeout=1200, build_url=None, project=None,
                             factory_properties=None):
     # Make sure the solution is not already there.
     if 'cros_deps' not in [s.name for s in self._solutions]:
       self._solutions.append(gclient_factory.GClientSolution(
           config.Master.trunk_url + '/src/tools/cros.DEPS', name='cros_deps'))
     return self.ChromiumFactory(target, clobber, tests, mode, slave_type,
                                 options, compile_timeout, build_url, project,
                                 factory_properties)