Pick the right download tool for windows.

bin/fetch-gn

 #!/usr/bin/env python
 
 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import subprocess
 import sys
 
 def quiet(*cmd):
   cmd = ' '.join(cmd).split()
   subprocess.check_output(cmd)
 
 def gn_path():
   if 'linux' in sys.platform:
     return 'buildtools/linux64/gn'
   if 'darwin' in sys.platform:
     return 'buildtools/mac/gn'
   return 'buildtools/win/gn.exe'
 
-quiet('download_from_google_storage',
+def download_tool():
+        if 'linux' in sys.platform or 'darwin' in sys.platform:
+                return 'download_from_google_storage'
+        return 'download_from_google_storage.bat'
+         
+quiet(download_tool(),
       '--no_resume --no_auth --bucket chromium-gn',
       '-s ', gn_path() + '.sha1')