[Android] Add support for external sharding to the test runner.

build/android/test_runner.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.
 
 """Runs all types of tests from one unified interface."""
 
 import argparse
 import collections
@@ skipping 45 matching lines @@
       '--num_retries', '--num-retries',
       dest='num_retries', type=int, default=2,
       help='Number of retries for a test before '
            'giving up (default: %(default)s).')
   parser.add_argument(
       '--test-launcher-summary-output',
       '--json-results-file',
       dest='json_results_file', type=os.path.realpath,
       help='If set, will dump results in JSON form '
            'to specified file.')
+  parser.add_argument(
+      '--test-launcher-shard-index',
+      type=int, default=os.environ.get('GTEST_SHARD_INDEX', 0),
+      help='Index of the external shard to run.')
+  parser.add_argument(
+      '--test-launcher-total-shards',
+      type=int, default=os.environ.get('GTEST_TOTAL_SHARDS', 1),
+      help='Total number of external shards.')
 
   return parser
 
 
 def AddTracingOptions(parser):
   # TODO(shenghuazhang): Move this into AddCommonOptions once it's supported
   # for all test types.
   parser.add_argument(
       '--trace-output',
       metavar='FILENAME', type=os.path.realpath,
@@ skipping 793 matching lines @@
     if e.is_infra_error:
       return constants.INFRA_EXIT_CODE
     return constants.ERROR_EXIT_CODE
   except: # pylint: disable=W0702
     logging.exception('Unrecognized error occurred.')
     return constants.ERROR_EXIT_CODE
 
 
 if __name__ == '__main__':
   sys.exit(main())