WebUI: Split unpack_pak functionality to its own GN action.

chrome/browser/resources/unpack_pak.py

 #!/usr/bin/env python
 # Copyright 2016 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 argparse
 import os
 import re
 import sys
 
 
 _HERE_PATH = os.path.join(os.path.dirname(__file__))
 
 
 _SRC_PATH = os.path.normpath(os.path.join(_HERE_PATH, '..', '..', '..'))
 sys.path.append(os.path.join(_SRC_PATH, 'tools', 'grit'))
@@ skipping 28 matching lines @@
   assert resource_filenames
 
   # Extract packed files, while preserving directory structure.
   for (resource_id, text) in data.resources.iteritems():
     filename = resource_filenames[resource_ids[resource_id]]
     dirname = os.path.join(out_path, os.path.dirname(filename))
     if not os.path.exists(dirname):
       os.makedirs(dirname)
     with open(os.path.join(out_path, filename), 'w') as file:
       file.write(text)
+
+
+def main():
+  parser = argparse.ArgumentParser()
+  parser.add_argument('--pak_file')
+  parser.add_argument('--out_folder')
+  args = parser.parse_args()
+
+  unpack(args.pak_file, args.out_folder)
+
+
+if __name__ == '__main__':
+  main()