[Android] Add repeat argument to UiRobot tests.

The test runner assumes that all tests ran in platform
mode of the args.repeat attribute. This is causing the
UiRobot tests to crash since they don't have this.

BUG=

Review URL: https://codereview.chromium.org/1415753002

Cr-Commit-Position: refs/heads/master@{#354901}
diff --git a/build/android/test_runner.py b/build/android/test_runner.py
index 955e09b..9ef3cd2 100755
--- a/build/android/test_runner.py
+++ b/build/android/test_runner.py
@@ -554,6 +554,9 @@
   group.add_argument('--app-under-test', required=True,
                      help='APK to run tests on.')
   group.add_argument(
+      '--repeat', dest='repeat', type=int, default=0,
+      help='Number of times to repeat the uirobot test.')
+  group.add_argument(
       '--minutes', default=5, type=int,
       help='Number of minutes to run uirobot test [default: %(default)s].')