gyp performance: don't invoke python to check dir existance

We spend a few tenths of a second every gyp invocation starting
the dir_exists.py program. Seems a bit unnecessary.

BUG=362075
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/234963003

git-svn-id: http://src.chromium.org/svn/trunk/src/build@264316 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -1316,8 +1316,8 @@
     # Contains data about the attached devices for gyp_managed_install.
     'build_device_config_path': '<(PRODUCT_DIR)/build_devices.cfg',
 
-    'sas_dll_exists': '<!(python <(DEPTH)/build/dir_exists.py "<(sas_dll_path)")',
-    'wix_exists': '<!(python <(DEPTH)/build/dir_exists.py "<(wix_path)")',
+    'sas_dll_exists': '<!pymod_do_main(dir_exists "<(sas_dll_path)")',
+    'wix_exists': '<!pymod_do_main(dir_exists "<(wix_path)")',
 
     'windows_sdk_default_path': '<(DEPTH)/third_party/platformsdk_win8/files',
     'directx_sdk_default_path': '<(DEPTH)/third_party/directxsdk/files',
@@ -1419,12 +1419,12 @@
       }, {
         'gcc_version%': 0,
       }],
-      ['OS=="win" and "<!(python <(DEPTH)/build/dir_exists.py <(windows_sdk_default_path))"=="True"', {
+      ['OS=="win" and "<!pymod_do_main(dir_exists <(windows_sdk_default_path))"=="True"', {
         'windows_sdk_path%': '<(windows_sdk_default_path)',
       }, {
         'windows_sdk_path%': 'C:/Program Files (x86)/Windows Kits/8.0',
       }],
-      ['OS=="win" and "<!(python <(DEPTH)/build/dir_exists.py <(directx_sdk_default_path))"=="True"', {
+      ['OS=="win" and "<!pymod_do_main(dir_exists <(directx_sdk_default_path))"=="True"', {
         'directx_sdk_path%': '<(directx_sdk_default_path)',
       }, {
         'directx_sdk_path%': '$(DXSDK_DIR)',

dir_exists.py

@@ -8,8 +8,16 @@ import os.path
 import sys
 
 def main():
-  sys.stdout.write(str(os.path.isdir(sys.argv[1])))
+  sys.stdout.write(_is_dir(sys.argv[1]))
   return 0
 
+def _is_dir(dir_name):
+  return str(os.path.isdir(dir_name))
+
+def DoMain(args):
+  """Hook to be called from gyp without starting a separate python
+  interpreter."""
+  return _is_dir(args[0])
+
 if __name__ == '__main__':
   sys.exit(main())