[Android] Add context manager to record logcat during step(s).

scripts/slave/recipes/android_webview_cts_tests.py

 # Copyright 2015 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.
 
 """
 Recipe for running WebView CTS using system WebView.
 """
 DEPS = [
   'adb',
   'bot_update',
@@ skipping 107 matching lines @@
           test_method.get('name') not in EXPECTED_FAILURE.get(class_name, [])):
         unexpected_test_failures.append(method_name)
 
   if unexpected_test_failures or not_executed_tests:
     api.step.active_result.presentation.status = api.step.FAILURE
     api.step.active_result.presentation.step_text += (
         api.test_utils.format_step_text(
             [['unexpected failures:', unexpected_test_failures],
              ['not executed:', not_executed_tests]]))
 
-  api.chromium_android.logcat_dump()
-  api.chromium_android.stack_tool_steps()
+  logcat_file = api.chromium.output_dir.join('full_logcat')
+  api.chromium_android.logcat_dump(output_logcat_file=logcat_file)
+  api.chromium_android.stack_tool_steps(logcat_file=logcat_file)
   api.chromium_android.test_report()
 
   if unexpected_test_failures:
     raise api.step.StepFailure("Unexpected Test Failures.")
   if not_executed_tests:
     raise api.step.StepFailure("Tests not executed.")
 
 def GenTests(api):
   result_xml_with_unexecuted_tests = """<TestResult>
                           <TestPackage>
@@ skipping 88 matching lines @@
       api.override_step_data('Read test result and report failures',
           api.raw_io.output(result_xml_with_unexpected_failure_method)) + \
       api.properties.generic(mastername='chromium.android')
 
   yield api.test('Test_parsing_invalid_cts_output') + \
       api.override_step_data('Run Cts', api.raw_io.stream_output(
           'Invalid CTS output here...',
           stream='stdout')) + \
       api.properties.generic(mastername='chromium.android') + \
       api.expect_exception('Exception')