android: actually allow running MANUAL_* gtests.

Change-Id: If8206c443eee80987c4528d6aaeb58fb348dc57b
Reviewed-on: https://chromium-review.googlesource.com/1176113Reviewed-by: Christian Fremerey <chfremer@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583346}

build/android/pylib/gtest/gtest_test_instance.py

@@ -533,7 +533,9 @@ class GtestTestInstance(test_instance.TestInstance):
     disabled_filter_items = []
 
     if disabled_prefixes is None:
-      disabled_prefixes = ['FAILS_', 'PRE_', 'MANUAL_']
+      disabled_prefixes = ['FAILS_', 'PRE_']
+      if '--run-manual' not in self._flags:
+        disabled_prefixes += ['MANUAL_']
       if not self._run_disabled:
         disabled_prefixes += ['DISABLED_', 'FLAKY_']