Update from https://crrev.com/304418

build/win_is_xtree_patched.py

+#!/usr/bin/env python
+# 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.
+
+"""Determines if the VS xtree header has been patched to disable C4702."""
+
+import os
+
+
+def IsPatched():
+  # TODO(scottmg): For now, just return if we're using the packaged toolchain
+  # script (because we know it's patched). Another case could be added here to
+  # query the active VS installation and actually check the contents of xtree.
+  # http://crbug.com/346399.
+  return os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', 1) == 0
+
+
+def DoMain(_):
+  """Hook to be called from gyp without starting a separate python
+  interpreter."""
+  return IsPatched()
+
+
+if __name__ == '__main__':
+  print DoMain([])