gn: Make WDK_DIR environment variable optional for VS professional users

build/vs_toolchain.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.
 
 import json
 import os
 import pipes
 import shutil
 import subprocess
 import sys
@@ skipping 154 matching lines @@
   previously updated by 'update'). This is used for the GN build."""
   SetEnvironmentAndGetRuntimeDllDirs()
   print '''vs_path = "%s"
 sdk_path = "%s"
 vs_version = "%s"
 wdk_dir = "%s"
 ''' % (
       os.environ['GYP_MSVS_OVERRIDE_PATH'],
       os.environ['WINDOWSSDKDIR'],
       os.environ['GYP_MSVS_VERSION'],
-      os.environ['WDK_DIR'])
+      os.environ.get('WDK_DIR', ''))
 
 
 def main():
   if not sys.platform.startswith(('win32', 'cygwin')):
     return 0
   commands = {
       'update': Update,
       'get_toolchain_dir': GetToolchainDir,
       # TODO(scottmg): Add copy_dlls for GN builds (gyp_chromium calls
       # CopyVsRuntimeDlls via import, currently).
   }
   if len(sys.argv) < 2 or sys.argv[1] not in commands:
     print >>sys.stderr, 'Expected one of: %s' % ', '.join(commands)
     return 1
   return commands[sys.argv[1]]()
 
 
 if __name__ == '__main__':
   sys.exit(main())