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

build/toolchain/mac/setup_toolchain.py

Index: build/toolchain/mac/setup_toolchain.py
diff --git a/build/toolchain/mac/setup_toolchain.py b/build/toolchain/mac/setup_toolchain.py
new file mode 100644
index 0000000000000000000000000000000000000000..431078fb1802d7f93adb310f8b917c4cc1c8162e
--- /dev/null
+++ b/build/toolchain/mac/setup_toolchain.py
@@ -0,0 +1,29 @@
+# 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 os
+import stat
+import sys
+
+def CopyTool(source_path):
+  """Copies the given tool to the current directory, including a warning not
+  to edit it."""
+  with open(source_path) as source_file:
+    tool_source = source_file.readlines()
+
+  # Add header and write it out to the current directory (which should be the
+  # root build dir).
+  out_path = 'gyp-mac-tool'
+  with open(out_path, 'w') as tool_file:
+    tool_file.write(''.join([tool_source[0],
+                             '# Generated by setup_toolchain.py do not edit.\n']
+                            + tool_source[1:]))
+  st = os.stat(out_path)
+  os.chmod(out_path, st.st_mode | stat.S_IEXEC)
+
+# Find the tool source, it's the first argument, and copy it.
+if len(sys.argv) != 2:
+  print "Need one argument (mac_tool source path)."
+  sys.exit(1)
+CopyTool(sys.argv[1])