[Android] Fall back to active_devices if the known device list file is empty.

build/android/pylib/perf/setup.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.
 
 """Generates test runner factory and tests for performance tests."""
 
 import json
 import fnmatch
 import logging
 import os
@@ skipping 10 matching lines @@
   # TODO(rnephew): Delete this when recipes change to pass file path.
   if not devices_path:
     logging.warning('Known devices file path not being passed. For device '
                     'affinity to work properly, it must be passed.')
     devices_path = os.path.join(os.environ.get('CHROMIUM_OUT_DIR', 'out'),
                                 device_list.LAST_DEVICES_FILENAME)
   try:
     if devices_path:
       devices = [device_utils.DeviceUtils(s)
                  for s in device_list.GetPersistentDeviceList(devices_path)]
+      if not devices and active_devices:
+        logging.warning('%s is empty. Falling back to active devices.',
+                        devices_path)
+        devices = active_devices
     else:
       logging.warning('Known devices file path not being passed. For device '
                       'affinity to work properly, it must be passed.')
       devices = active_devices
   except IOError as e:
     logging.error('Unable to find %s [%s]', devices_path, e)
     devices = active_devices
   return sorted(devices)
 
 
@@ skipping 55 matching lines @@
   if test_options.flaky_steps:
     with file(test_options.flaky_steps, 'r') as f:
       flaky_steps = json.load(f)
 
   def TestRunnerFactory(device, shard_index):
     return test_runner.TestRunner(
         test_options, device, shard_index, len(all_devices),
         steps_dict, flaky_steps)
 
   return (TestRunnerFactory, sorted_step_names, all_devices)