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

scripts/slave/recipes/chromium.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.
 
 DEPS = [
   'adb',
   'bisect_tester',
   'chromium',
   'chromium_android',
   'chromium_tests',
@@ skipping 14 matching lines @@
   mastername = api.properties.get('mastername')
   buildername = api.properties.get('buildername')
 
   if mastername == 'tryserver.chromium.perf' and api.chromium_tests.builders[
       mastername]['builders'][buildername]['bot_type'] == 'tester':
     api.bisect_tester.upload_job_url()
 
   api.chromium_tests.configure_build(mastername, buildername)
   update_step, master_dict, test_spec = \
       api.chromium_tests.prepare_checkout(mastername, buildername)
+
+  tests = api.chromium_tests.tests_for_builder(
+      mastername, buildername, update_step, master_dict)
+
+  api.chromium.run_mb_if_necessary(mastername, buildername, tests)
+
   api.chromium_tests.compile(mastername, buildername, update_step, master_dict,
                              test_spec)
-  tests = api.chromium_tests.tests_for_builder(
-      mastername, buildername, update_step, master_dict)
 
   if not tests:
     return
 
   api.chromium_tests.configure_swarming('chromium', precommit=False,
                                         mastername=mastername)
   test_runner = api.chromium_tests.create_test_runner(api, tests)
   with api.chromium_tests.wrap_chromium_tests(mastername):
     test_runner()
 
@@ skipping 400 matching lines @@
     api.properties.generic(
         mastername='chromium.webkit',
         buildername='WebKit XP',
         project='chromium',
         parent_buildername='WebKit Win Builder',
         parent_got_revision='1e74b372f951d4491f305ec64f6decfcda739e73',
         parent_got_webkit_revision='191269',
         revision='1e74b372f951d4491f305ec64f6decfcda739e73') +
     api.platform('win', 32)
   )