Add a --force flag to get_toolchain_if_necessary.py to let it run on non-Windows.

win_toolchain/get_toolchain_if_necessary.py

 #!/usr/bin/env python
 # 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.
 
 """Downloads and unpacks a toolchain for building on Windows. The contents are
 matched by sha1 which will be updated when the toolchain is updated.
 
 Having a toolchain script in depot_tools means that it's not versioned
 directly with the source code. That is, if the toolchain is upgraded, but
@@ skipping 195 matching lines @@
   temp_dir, local_zip = DownloadUsingGsutil(tree_sha1 + '.zip')
   sys.stdout.write('Extracting %s...\n' % local_zip)
   sys.stdout.flush()
   with zipfile.ZipFile(local_zip, 'r', zipfile.ZIP_DEFLATED, True) as zf:
     zf.extractall(target_dir)
   if temp_dir:
     RmDir(temp_dir)
 
 
 def main():
-  if not sys.platform.startswith(('cygwin', 'win32')):
-    return 0
-
   parser = optparse.OptionParser(description=sys.modules[__name__].__doc__)
   parser.add_option('--output-json', metavar='FILE',
                     help='write information about toolchain to FILE')
+  parser.add_option('--force', action='store_true',
+                    help='force script to run on non-Windows hosts')
   options, args = parser.parse_args()
 
+  if not (sys.platform.startswith(('cygwin', 'win32')) or options.force):
+    return 0
+
   if sys.platform == 'cygwin':
     # This script requires Windows Python, so invoke with depot_tools' Python.
     def winpath(path):
       return subprocess.check_output(['cygpath', '-w', path]).strip()
     python = os.path.join(DEPOT_TOOLS_PATH, 'python.bat')
     cmd = [python, winpath(__file__)]
     if options.output_json:
       cmd.extend(['--output-json', winpath(options.output_json)])
     cmd.extend(args)
     sys.exit(subprocess.call(cmd))
@@ skipping 88 matching lines @@
 
   if options.output_json:
     shutil.copyfile(os.path.join(target_dir, '..', 'data.json'),
                     options.output_json)
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())