Add a snapshot of flutter/engine/src/build to our sdk

build/dir_exists.py

Index: build/dir_exists.py
diff --git a/build/dir_exists.py b/build/dir_exists.py
new file mode 100755
index 0000000000000000000000000000000000000000..70d367ec2690730f6318c4d8373750db5bb70fcd
--- /dev/null
+++ b/build/dir_exists.py
@@ -0,0 +1,23 @@
+#!/usr/bin/env python
+# Copyright (c) 2011 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.
+"""Writes True if the argument is a directory."""
+
+import os.path
+import sys
+
+def main():
+  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())