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

build/android/test_runner.py

Index: build/android/test_runner.py
diff --git a/build/android/test_runner.py b/build/android/test_runner.py
index ee6f87a86a0a382a7be1b30054c5a1617c1cb61e..b3c1b97180c03ffb1e5ad5f1d16e0347de5f09a3 100755
--- a/build/android/test_runner.py
+++ b/build/android/test_runner.py
@@ -63,6 +63,14 @@ def AddTestLauncherArgs(parser):
       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