Revert r136547 "Enforce VS2010 on trunk."

build/gyp_chromium

 #!/usr/bin/env python
 
 # Copyright (c) 2011 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.
 
 # This script is wrapper for Chromium that adds some support for how GYP
 # is invoked by Chromium beyond what can be done in the gclient hooks.
 
 import glob
@@ skipping 89 matching lines @@
   return result
 
 if __name__ == '__main__':
   args = sys.argv[1:]
 
   # Use the Psyco JIT if available.
   if psyco:
     psyco.profile()
     print "Enabled Psyco JIT."
 
-  os.environ['GYP_MSVS_VERSION'] = '2010'
-
   # Fall back on hermetic python if we happen to get run under cygwin.
   # TODO(bradnelson): take this out once this issue is fixed:
   #    http://code.google.com/p/gyp/issues/detail?id=177
   if sys.platform == 'cygwin':
     python_dir = os.path.join(chrome_src, 'third_party', 'python_26')
     env = os.environ.copy()
     env['PATH'] = python_dir + os.pathsep + env.get('PATH', '')
     p = subprocess.Popen(
        [os.path.join(python_dir, 'python.exe')] + sys.argv,
        env=env, shell=False)
@@ skipping 42 matching lines @@
   # to enfore syntax checking.
   syntax_check = os.environ.get('CHROMIUM_GYP_SYNTAX_CHECK')
   if syntax_check and int(syntax_check):
     args.append('--check')
 
   print 'Updating projects from gyp files...'
   sys.stdout.flush()
 
   # Off we go...
   sys.exit(gyp.main(args))