[android] Use contextlib_ext.Optional for conditional context managers.

build/android/test_runner.py

 #!/usr/bin/env python
 #
 # 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.
 
 """Runs all types of tests from one unified interface."""
 
 import argparse
 import collections
@@ skipping 21 matching lines @@
 from pylib.base import base_test_result
 from pylib.base import environment_factory
 from pylib.base import test_dispatcher
 from pylib.base import test_instance_factory
 from pylib.base import test_run_factory
 from pylib.constants import host_paths
 from pylib.linker import setup as linker_setup
 from pylib.results import json_results
 from pylib.results import report_results
 
+from py_utils import contextlib_ext
+
 
 _DEVIL_STATIC_CONFIG_FILE = os.path.abspath(os.path.join(
     host_paths.DIR_SOURCE_ROOT, 'build', 'android', 'devil_config.json'))
 
 
 def AddCommonOptions(parser):
   """Adds all common options to |parser|."""
 
   group = parser.add_argument_group('Common Options')
 
@@ skipping 686 matching lines @@
   # while each list of TestRunResults contains all tries in a single
   # iteration.
   all_raw_results = []
 
   # all_iteration_results is a list of base_test_result.TestRunResults
   # objects. Each instance of TestRunResults contains the last test
   # result for each test run in that iteration.
   all_iteration_results = []
 
   @contextlib.contextmanager
-  def noop():
-    yield
+  def write_json_file():
+    try:
+      yield
+    finally:
+      json_results.GenerateJsonResultsFile(
+          all_raw_results, args.json_results_file)
 
-  json_writer = noop()
-  if args.json_results_file:
-    @contextlib.contextmanager
-    def write_json_file():
-      try:
-        yield
-      finally:
-        json_results.GenerateJsonResultsFile(
-            all_raw_results, args.json_results_file)
-
-    json_writer = write_json_file()
+  json_writer = contextlib_ext.Optional(
+      write_json_file(),
+      args.json_results_file)
 
   ### Set up test objects.
 
   env = environment_factory.CreateEnvironment(args, infra_error)
   test_instance = test_instance_factory.CreateTestInstance(args, infra_error)
   test_run = test_run_factory.CreateTestRun(
       args, env, test_instance, infra_error)
 
   ### Run.
 
@@ skipping 116 matching lines @@
     if e.is_infra_error:
       return constants.INFRA_EXIT_CODE
     return constants.ERROR_EXIT_CODE
   except: # pylint: disable=W0702
     logging.exception('Unrecognized error occurred.')
     return constants.ERROR_EXIT_CODE
 
 
 if __name__ == '__main__':
   sys.exit(main())