Subprocess uses shell=True on Windows when launching GN.

git_cl.py

 #!/usr/bin/env python
 # 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld and Gerrit."""
 
 from distutils.version import LooseVersion
@@ skipping 77 matching lines @@
   sys.exit(1)
 
 
 def GetNoGitPagerEnv():
   env = os.environ.copy()
   # 'cat' is a magical git string that disables pagers on all platforms.
   env['GIT_PAGER'] = 'cat'
   return env
 
 
-def RunCommand(args, error_ok=False, error_message=None, **kwargs):
+def RunCommand(args, error_ok=False, error_message=None, shell=False, **kwargs):
   try:
-    return subprocess2.check_output(args, shell=False, **kwargs)
+    return subprocess2.check_output(args, shell=shell, **kwargs)
   except subprocess2.CalledProcessError as e:
     logging.debug('Failed running %s', args)
     if not error_ok:
       DieWithError(
           'Command "%s" failed.\n%s' % (
             ' '.join(args), error_message or e.stdout or ''))
     return e.stdout
 
 
 def RunGit(args, **kwargs):
@@ skipping 4630 matching lines @@
       print ('Warning: Unable to check Dart code formatting. Dart SDK not ' +
              'found in this checkout. Files in other languages are still ' +
              'formatted.')
 
   # Format GN build files. Always run on full build files for canonical form.
   if gn_diff_files:
     cmd = ['gn', 'format']
     if not opts.dry_run and not opts.diff:
       cmd.append('--in-place')
     for gn_diff_file in gn_diff_files:
-      stdout = RunCommand(cmd + [gn_diff_file], cwd=top_dir)
+      stdout = RunCommand(cmd + [gn_diff_file],
+                          shell=sys.platform == 'win32',
+                          cwd=top_dir)
       if opts.diff:
         sys.stdout.write(stdout)
 
   return return_value
 
 
 @subcommand.usage('<codereview url or issue id>')
 def CMDcheckout(parser, args):
   """Checks out a branch associated with a given Rietveld or Gerrit issue."""
   _, args = parser.parse_args(args)
@@ skipping 93 matching lines @@
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   setup_color.init()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)