Change the way to detect build slave.

gclient.py

 #!/usr/bin/python
 # Copyright (c) 2010 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.
 
 """Meta checkout manager supporting both Subversion and GIT.
 
 Files
   .gclient      : Current client configuration, written by 'config' command.
                   Format is a Python script defining 'solutions', a list whose
@@ skipping 1158 matching lines @@
 def Main(argv):
   """Doesn't parse the arguments here, just find the right subcommand to
   execute."""
   try:
     # Do it late so all commands are listed.
     CMDhelp.usage = ('\n\nCommands are:\n' + '\n'.join([
         '  %-10s %s' % (fn[3:], Command(fn[3:]).__doc__.split('\n')[0].strip())
         for fn in dir(sys.modules[__name__]) if fn.startswith('CMD')]))
     parser = optparse.OptionParser(version='%prog ' + __version__)
     # TODO(maruel): Temporary workaround to disable parallel checkout on
-    # buildbots until they can correctly parse its output. Uses that fact that
-    # stdout is redirected as a signal.
-    if sys.stdout.isatty():
+    # buildbots until they can correctly parse its output. stdout being
+    # redirected is not a good signal, at least on linux. Check for environment
+    # variable instead.
+    if 'CHROME_HEADLESS' not in os.environ:
       jobs = 8
     else:
       jobs = 1
     parser.add_option('-j', '--jobs', default=jobs, type='int',
                       help='Specify how many SCM commands can run in parallel; '
                            'default=%default')
     parser.add_option('-v', '--verbose', action='count', default=0,
                       help='Produces additional output for diagnostics. Can be '
                            'used up to three times for more logging info.')
     parser.add_option('--gclientfile', dest='config_filename',
@@ skipping 45 matching lines @@
     return CMDhelp(parser, argv)
   except gclient_utils.Error, e:
     print >> sys.stderr, 'Error: %s' % str(e)
     return 1
 
 
 if '__main__' == __name__:
   sys.exit(Main(sys.argv[1:]))
 
 # vim: ts=2:sw=2:tw=80:et: