Add GN support for midl.

build/toolchain/win/setup_toolchain.py

 # Copyright (c) 2013 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 errno
 import os
 import re
 import subprocess
 import sys
 
 """
 Copies the given "win tool" (which the toolchain uses to wrap compiler
 invocations) and the environment blocks for the 32-bit and 64-bit builds on
 Windows to the build directory.
 
 The arguments are the visual studio install location and the location of the
 win tool. The script assumes that the root build directory is the current dir
 and the files will be written to the current directory.
 """
 
 
 def ExtractImportantEnvironment():
   """Extracts environment variables required for the toolchain from the
   current environment."""
   envvars_to_save = (
       'goma_.*',  # TODO(scottmg): This is ugly, but needed for goma.
+      'include',  # Needed by midl compiler.

[scottmg, 2014/06/17 20:32:40]

ah, you found one!

       'path',
       'pathext',
       'systemroot',
       'temp',
       'tmp',
       )
   result = {}
   for envvar in envvars_to_save:
     if envvar in os.environ:
       envvar = envvar.lower()
@@ skipping 61 matching lines @@
   env_file.write(environ)
 
 # Add 64-bit compiler path to the beginning and write the block.
 path64 = [os.path.join(vs_path, "VC\\BIN\\amd64")] + \
          [os.path.join(win_sdk_path, "bin\\x64")] + \
          path
 important_env_vars["PATH"] = ";".join(path64)
 environ = FormatAsEnvironmentBlock(important_env_vars)
 with open('environment.x64', 'wb') as env_file:
   env_file.write(environ)