[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 952fca3fd650091b513917bb5e20a7c0d37f24e1..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
 
@@ -162,11 +170,6 @@ def ProcessCommonOptions(args):
   if args.output_directory:
     constants.SetOutputDirectory(args.output_directory)
 
-  # Some things such as Forwarder require ADB to be in the environment path.
-  adb_dir = os.path.dirname(constants.GetAdbPath())
-  if adb_dir and adb_dir not in os.environ['PATH'].split(os.pathsep):
-    os.environ['PATH'] = adb_dir + os.pathsep + os.environ['PATH']
-
 
 def AddDeviceOptions(parser):
   """Adds device options to |parser|."""