[Android] Add gn support for multidex.

build/android/gyp/dex.py

 #!/usr/bin/env python
 #
 # Copyright 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 json
 import logging
 import optparse
 import os
@@ skipping 42 matching lines @@
                     action='store_true',
                     help='Enable incremental builds when possible.')
   parser.add_option('--inputs', help='A list of additional input paths.')
   parser.add_option('--excluded-paths',
                     help='A list of paths to exclude from the dex file.')
   parser.add_option('--main-dex-list-path',
                     help='A file containing a list of the classes to '
                          'include in the main dex.')
   parser.add_option('--multidex-configuration-path',
                     help='A JSON file containing multidex build configuration.')
+  parser.add_option('--multi-dex', default=False, action='store_true',
+                    help='Generate multiple dex files.')
 
   options, paths = parser.parse_args(args)
 
   required_options = ('android_sdk_tools',)
   build_utils.CheckOptions(options, parser, required=required_options)
 
-  options.multi_dex = False
   if options.multidex_configuration_path:
     with open(options.multidex_configuration_path) as multidex_config_file:
       multidex_config = json.loads(multidex_config_file.read())
     options.multi_dex = multidex_config.get('enabled', False)
 
   if options.multi_dex and not options.main_dex_list_path:
     logging.warning('multidex cannot be enabled without --main-dex-list-path')
     options.multi_dex = False
   elif options.main_dex_list_path and not options.multi_dex:
     logging.warning('--main-dex-list-path is unused if multidex is not enabled')
@@ skipping 105 matching lines @@
       options,
       input_paths=input_paths,
       input_strings=dex_cmd,
       output_paths=output_paths,
       force=force,
       pass_changes=True)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))