Teach dart_package to understand the packages/ subdirectory

mojo/public/tools/dart_list_packages_contents.py

+#!/usr/bin/python
+# 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.
+
+"""This script outputs the filenames of the files that are in the "packages/"
+subdir of the given directory, relative to that directory."""
+
+import argparse
+import os
+import sys
+
+def main(target_directory):
+  os.chdir(target_directory)
+  for root, _, files in os.walk("packages", followlinks=True):
+    for f in files:
+      print os.path.join(root, f)
+
+if __name__ == '__main__':
+  parser = argparse.ArgumentParser(
+      description="List filenames of files in the packages/ subdir of the "
+                  "given directory.")
+  parser.add_argument("--target-directory",
+                      dest="target_directory",
+                      metavar="<target-directory>",
+                      type=str,
+                      required=True,
+                      help="The target directory, specified relative to this "
+                           "directory.")
+  args = parser.parse_args()
+  sys.exit(main(args.target_directory))