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

scripts/slave/recipe_modules/chromium_android/config.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.
 
 import types
 
 from recipe_engine.config import config_item_context, ConfigGroup
 from recipe_engine.config import ConfigList, Dict, List, Single, Static
 from recipe_engine.config_types import Path
 
@@ skipping 11 matching lines @@
     run_tree_truth = Single(bool, required=False, empty_val=True),
     deps_file = Single(basestring, required=False, empty_val='.DEPS.git'),
     internal_dir_name = Single(basestring, required=False),
     # deps_dir: where to checkout the gclient deps file
     deps_dir = Single(basestring, required=False, empty_val=REPO_NAME),
     managed = Single(bool, required=False, empty_val=True),
     extra_deploy_opts = List(inner_type=basestring),
     tests = List(inner_type=basestring),
     cr_build_android = Static(Path('[CHECKOUT]', 'build', 'android')),
     test_runner = Single(Path),
+    default_logcat_dir = Single(Path),
     gclient_custom_deps = Dict(value_type=(basestring, types.NoneType)),
     channel = Single(basestring, empty_val='chrome'),
     gclient_custom_vars = Dict(value_type=(basestring, types.NoneType)),
     coverage = Single(bool, required=False, empty_val=False),
     chrome_specific_wipe = Single(bool, required=False, empty_val=False),
     incremental_coverage = Single(bool, required=False, empty_val=False),
     env = ConfigGroup(
       LLVM_FORCE_HEAD_REVISION = Single(basestring, required=False),
     ),
     gce_setup = Single(bool, required=False, empty_val=False),
   )
 
 
 config_ctx = config_item_context(BaseConfig)
 
 @config_ctx(is_root=True)
 def base_config(c):
+  c.default_logcat_dir = Path('[CHECKOUT]', 'out', 'logcat_dir')
   c.internal_dir_name = 'clank'
   c.test_runner = Path('[CHECKOUT]', 'build', 'android', 'test_runner.py')
 
 @config_ctx()
 def main_builder(c):
   pass
 
 @config_ctx()
 def clang_builder(c):
   pass
@@ skipping 138 matching lines @@
 def webview_perf(c):
   pass
 
 @config_ctx()
 def cast_builder(c):
   pass
 
 @config_ctx(includes=['x86_builder'])
 def gce_builder(c):
   c.gce_setup = True