Fix KeyError caused when filtering gtests on multiple threads.

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

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import collections
 import itertools
 import logging
 import os
 import posixpath
 
@@ skipping 320 matching lines @@
     @local_device_environment.handle_shard_failures_with(
         on_failure=self._env.BlacklistDevice)
     def list_tests(dev):
       raw_test_list = self._delegate.Run(
           None, dev, flags='--gtest_list_tests', timeout=30)
       tests = gtest_test_instance.ParseGTestListTests(raw_test_list)
       if not tests:
         logging.info('No tests found. Output:')
         for l in raw_test_list:
           logging.info('  %s', l)
-      tests = self._test_instance.FilterTests(tests)
       return tests
 
-    # Query all devices in case one fails.
+    # Query all devices in case one fails. Return unfiltered test list
+    # because |FilterTests| function is not threadsafe on older versions
+    # of python due to its use of |fnmatch| module.
     test_lists = self._env.parallel_devices.pMap(list_tests).pGet(None)
-
+    test_lists = [self._test_instance.FilterTests(tests)

[jbudorick, 2016/11/17 00:16:03]

This change is ok, but it should also either:
 - make FilterTests threadsafe
 - add a comment in FilterTests's docstring explaining that it isn't threadsafe
and why.

+                  for tests in test_lists]
     # If all devices failed to list tests, raise an exception.
     # Check that tl is not None and is not empty.
     if all(not tl for tl in test_lists):
       raise device_errors.CommandFailedError(
           'Failed to list tests on any device')
     return list(sorted(set().union(*[set(tl) for tl in test_lists if tl])))
 
   #override
   def _RunTest(self, device, test):
     # Run the test.
@@ skipping 41 matching lines @@
   def TearDown(self):
     @local_device_environment.handle_shard_failures
     def individual_device_tear_down(dev):
       for s in self._servers.get(str(dev), []):
         s.TearDown()
 
       tool = self.GetTool(dev)
       tool.CleanUpEnvironment()
 
     self._env.parallel_devices.pMap(individual_device_tear_down)