Don't import win32gui when it's not needed

chrome/test/data/native_messaging/native_hosts/echo.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.
 
 # A simple native client in python.
 # All this client does is echo the text it receives back at the extension.
 
 import os
 import platform
@@ skipping 20 matching lines @@
     return 1
   # TODO(sergeyu): Use argparse module to parse the arguments (not available in
   # Python 2.6).
   for arg in sys.argv[1:]:
     if arg.startswith('--'):
       if arg.startswith('--parent-window='):
         parent_window = long(arg[len('--parent-window='):])
     elif caller_url == None:
       caller_url = arg
 
-  if platform.system() == 'Windows':
+  if platform.system() == 'Windows' and parent_window:
     import win32gui
-    if parent_window and not win32gui.IsWindow(parent_window):
+    if not win32gui.IsWindow(parent_window):
       sys.stderr.write('Invalid --parent-window.\n')
       return 1
 
   while 1:
     # Read the message type (first 4 bytes).
     text_length_bytes = sys.stdin.read(4)
 
     if len(text_length_bytes) == 0:
       break
 
@@ skipping 23 matching lines @@
 
     message_number += 1
 
     message = '{{"id": {0}, "echo": {1}, "caller_url": "{2}"}}'.format(
           message_number, text, caller_url).encode('utf-8')
     if not WriteMessage(message):
       break
 
 if __name__ == '__main__':
   sys.exit(Main())