Use shell=False on non-Windows for gn-format.py

tools/gn/bin/gn-format.py

 # Copyright 2014 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.
 #
 # Based on clang-format.py.
 #
 # This file is a minimal gn format vim-integration. To install:
 # - Change 'binary' if gn is not on the path (see below).
 # - Add to your .vimrc:
 #
 #   map <F1> :pyf <path-to-this-file>/gn-format.py<CR>
 #
 # gn format currently formats only a complete file so visual ranges, etc. won't
 # be used. It operates on the current, potentially unsaved buffer and does not
 # create or save any files. To revert a formatting, just undo.
 
 import difflib
 import subprocess
 import sys
 import vim
 
 # Change this to the full path if gn is not on the path.
 binary = 'gn'
 
 def main():
   # Get the current text.
   buf = vim.current.buffer
   text = '\n'.join(buf)
 
+  is_win = sys.platform.startswith('win32')
   # Avoid flashing an ugly cmd prompt on Windows when invoking gn.
   startupinfo = None
-  if sys.platform.startswith('win32'):
+  if is_win:
     startupinfo = subprocess.STARTUPINFO()
     startupinfo.dwFlags |= subprocess.STARTF_USESHOWWINDOW
     startupinfo.wShowWindow = subprocess.SW_HIDE
 
-  # Call formatter.
+  # Call formatter. Needs shell=True on Windows due to gn.bat in depot_tools.
   p = subprocess.Popen([binary, 'format', '--stdin'],
                        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                        stdin=subprocess.PIPE, startupinfo=startupinfo,
-                       shell=True, universal_newlines=True)
+                       shell=is_win, universal_newlines=True)
   stdout, stderr = p.communicate(input=text)
   if p.returncode != 0:
     print 'Formatting failed, please report to gn-dev@chromium.org.'
     print stdout, stderr
   else:
     # Otherwise, replace current buffer.
     lines = stdout.split('\n')
     # Last line should have trailing \n, but we don't want to insert a blank
     # line at the end of the buffer, so remove that.
     if lines[-1] == '':
       lines = lines[:-1]
     sequence = difflib.SequenceMatcher(None, vim.current.buffer, lines)
     for op in reversed(sequence.get_opcodes()):
       if op[0] is not 'equal':
         vim.current.buffer[op[1]:op[2]] = lines[op[3]:op[4]]
 
 main()