Add swarming support for MB (and the GN bots) in the chromium recipes.

scripts/slave/recipes/chromium_trybot.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.
 
 from infra.libs.infra_types import freeze
 
 DEPS = [
   'bot_update',
   'chromium',
   'chromium_android',
@@ skipping 403 matching lines @@
     tests.append(api.chromium_tests.steps.BlinkTest())
 
   compile_targets, tests_including_triggered = \
       api.chromium_tests.get_compile_targets_and_tests(
           bot_config['mastername'],
           bot_config['buildername'],
           master_dict,
           override_bot_type='builder_tester',
           override_tests=tests)
 
+  api.m.chromium.run_mb_if_necessary(mastername, buildername,
+                                     tests_including_triggered)
+
   requires_compile, matching_exes, compile_targets = \
       api.chromium_tests.analyze(
           affected_files,
           all_compile_targets(api, tests + tests_including_triggered),
           compile_targets,
           'trybot_analyze_config.json')
 
   if not requires_compile:
     return
 
@@ skipping 555 matching lines @@
 
   yield (
     api.test('swarming_paths') +
     api.properties.tryserver(
       mastername='tryserver.chromium.linux',
       buildername='linux_chromium_rel_ng',
       path_config='swarming',
     ) +
     api.platform.name('linux')
   )