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

build/android/pylib/instrumentation/instrumentation_test_instance.py

Index: build/android/pylib/instrumentation/instrumentation_test_instance.py
diff --git a/build/android/pylib/instrumentation/instrumentation_test_instance.py b/build/android/pylib/instrumentation/instrumentation_test_instance.py
index 93e3a63380d72855f60dfc0246adb3c5c774e230..1824537b00bbe2efedc4f1e2bc8b12dabfa57b21 100644
--- a/build/android/pylib/instrumentation/instrumentation_test_instance.py
+++ b/build/android/pylib/instrumentation/instrumentation_test_instance.py
@@ -504,6 +504,9 @@ class InstrumentationTestInstance(test_instance.TestInstance):
     self._edit_shared_prefs = []
     self._initializeEditPrefsAttributes(args)
 
+    self._external_shard_index = args.test_launcher_shard_index
+    self._total_external_shards = args.test_launcher_total_shards
+
   def _initializeApkAttributes(self, args, error_func):
     if args.apk_under_test:
       apk_under_test_path = args.apk_under_test
@@ -734,6 +737,10 @@ class InstrumentationTestInstance(test_instance.TestInstance):
     return self._edit_shared_prefs
 
   @property
+  def external_shard_index(self):
+    return self._external_shard_index
+
+  @property
   def flags(self):
     return self._flags
 
@@ -789,6 +796,10 @@ class InstrumentationTestInstance(test_instance.TestInstance):
   def timeout_scale(self):
     return self._timeout_scale
 
+  @property
+  def total_external_shards(self):
+    return self._total_external_shards
+
   #override
   def TestType(self):
     return 'instrumentation'