[Android] Ensure perf test runner does not create shards for blacklisted devices.

build/android/pylib/base/test_dispatcher.py

 # Copyright 2013 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.
 
 """Dispatches tests, either sharding or replicating them.
 
 Performs the following steps:
 * Create a test collection factory, using the given tests
   - If sharding: test collection factory returns the same shared test collection
     to all test runners
@@ skipping 129 matching lines @@
     runner_factory: Callable that takes a device and index and returns a
       TestRunner object.
     device: The device serial number to set up.
     out_runners: List to add the successfully set up TestRunner object.
     threadsafe_counter: A _ThreadSafeCounter object used to get shard indices.
   """
   try:
     index = threadsafe_counter.GetAndIncrement()
     logging.warning('Creating shard %s for device %s.', index, device)
     runner = runner_factory(device, index)
-    runner.SetUp()
-    out_runners.append(runner)
+    if runner:

[jbudorick, 2016/06/07 00:27:26]

Nit: remove the logging from the runner_factory and log something at warning
level in an else block here.

[rnephew (Reviews Here), 2016/06/07 00:40:31]

Done.

+      runner.SetUp()
+      out_runners.append(runner)
   except (device_errors.CommandFailedError,
           device_errors.CommandTimeoutError,
           device_errors.DeviceUnreachableError):
     logging.exception('Failed to create shard for %s', str(device))
 
 
 def _RunAllTests(runners, test_collection_factory, num_retries, timeout=None,
                  tag_results_with_device=False):
   """Run all tests using the given TestRunners.
 
@@ skipping 168 matching lines @@
   try:
     return _RunAllTests(runners, test_collection_factory,
                         num_retries, test_timeout, tag_results_with_device)
   finally:
     try:
       _TearDownRunners(runners, setup_timeout)
     except device_errors.DeviceUnreachableError as e:
       logging.warning('Device unresponsive during TearDown: [%s]', e)
     except Exception: # pylint: disable=broad-except
       logging.exception('Unexpected exception caught during TearDown')