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

build/android/pylib/local/device/local_device_test_run.py

Index: build/android/pylib/local/device/local_device_test_run.py
diff --git a/build/android/pylib/local/device/local_device_test_run.py b/build/android/pylib/local/device/local_device_test_run.py
index 1d7ebdf802802258f1c5d275e0b60b69913db8f2..5288fb32be32eade57e06725ff1948cd94d87f37 100644
--- a/build/android/pylib/local/device/local_device_test_run.py
+++ b/build/android/pylib/local/device/local_device_test_run.py
@@ -177,6 +177,11 @@ class LocalDeviceTestRun(test_run.TestRun):
 
     return [t for t in failed_tests if self._ShouldRetry(t)]
 
+  def _ApplyExternalSharding(self, tests, shard_index, total_shards):
+    return [
+        t for t in tests
+        if hash(self._GetUniqueTestName(t)) % total_shards == shard_index]
+
   def GetTool(self, device):
     if not str(device) in self._tools:
       self._tools[str(device)] = valgrind_tools.CreateTool(