Fix build_command_buffer for Windows

tools/build_command_buffer.py

 #!/usr/bin/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.
 
 
 """
 Script to build the command buffer shared library and copy it to Skia tree
@@ skipping 117 matching lines @@
     except subprocess.CalledProcessError as error:
       sys.exit('Error (ret code: %s) calling "%s" in %s' % (error.returncode,
           error.cmd, chrome_src_dir))
 
   try:
     subprocess.check_call([gclient, 'runhooks'], cwd=chrome_src_dir)
   except subprocess.CalledProcessError as error:
     sys.exit('Error (ret code: %s) calling "%s" in %s' % (
         error.returncode, error.cmd, chrome_src_dir))
 
+  gn = 'gn'
   platform = 'linux64'
   if sys.platform == 'darwin':
     platform = 'mac'
   elif sys.platform == 'win32':
     platform = 'win'
-  gn = os.path.join(chrome_src_dir, 'buildtools', platform, 'gn')
+    gn = 'gn.exe'
+  gn = os.path.join(chrome_src_dir, 'buildtools', platform, gn)
   try:
     subprocess.check_call([gn, 'gen', chrome_target_dir_rel],
                           cwd=chrome_src_dir)
   except subprocess.CalledProcessError as error:
     sys.exit('Error (ret code: %s) calling "%s" in %s' % (
         error.returncode, error.cmd, chrome_src_dir))
 
   try:
     subprocess.check_call(['ninja'] + shlex.split(args.extra_ninja_args) +
         ['-C', chrome_target_dir_rel, 'command_buffer_gles2'],
@@ skipping 19 matching lines @@
 
   if not os.path.isfile(shared_lib_dst):
     sys.exit('Command buffer library not copied to ' + shared_lib_dst)
 
   print('Command buffer library copied to ' + shared_lib_dst)
 
 
 if __name__ == '__main__':
   main()