Unify mc.exe calling in GN, set environment.

build/win/message_compiler.py

Index: build/win/message_compiler.py
diff --git a/build/win/message_compiler.py b/build/win/message_compiler.py
new file mode 100644
index 0000000000000000000000000000000000000000..5e52efe8ca871e1ec29aa13243083c9758f2f286
--- /dev/null
+++ b/build/win/message_compiler.py
@@ -0,0 +1,26 @@
+# Copyright 2015 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.
+
+# Runs the Microsoft Message Compiler (mc.exe). This Python adapter is for the
+# GN build, which can only run Python and not native binaries.
+#
+# Usage: message_compiler.py <environment_file> [<args to mc.exe>*]
+
+import subprocess
+import sys
+
+# Read the environment block from the file. This is stored in the format used
+# by CreateProcess. Drop last 2 NULs, one for list terminator, one for trailing
+# vs. separator.
+env_pairs = open(sys.argv[1]).read()[:-2].split('\0')
+env_dict = dict([item.split('=', 1) for item in env_pairs])
+
+# mc writes to stderr, so this explicitly redirects to stdout and eats it.
+try:
+  subprocess.check_output(["mc.exe"] + sys.argv[2:],
+                          env=env_dict,
+                          stderr=subprocess.STDOUT)
+except subprocess.CalledProcessError as e:
+  print e.output
+  sys.exit(e.returncode)