Pass mb_mastername and mb_buildername as parameters to override the default.

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',
   'amp',
   'bisect_tester',
   'bot_update',
   'chromium',
@@ skipping 25 matching lines @@
 
 def RunSteps(api):
   # build/tests/masters_recipes_tests.py needs to manipulate the BUILDERS
   # dict, so we provide an API to dump it here.
   if api.properties.get('dump_builders'):  # pragma: no cover
     api.file.write(
         'Dump BUILDERS dict', api.properties['dump_builders'],
         api.json.dumps(api.chromium_tests.builders, default=ignore_undumpable))
     return
 
-  mastername = api.properties.get('mastername')
-  buildername = api.properties.get('buildername')
+  mastername = api.properties['mastername']
+  buildername = api.properties['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)
   api.chromium_tests.compile(mastername, buildername, update_step, master_dict,
-                             test_spec)
+                             test_spec, mb_mastername=mastername,
+                             mb_buildername=buildername)
   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, tests):
@@ skipping 659 matching lines @@
     api.test('amp_split_recipe_collect_failure') +
     api.properties(
         mastername='chromium.fyi',
         buildername='Android Tests (amp split)',
         slavename='build1-a1',
         buildnumber='77457',
         parent_build_archive_url='gs://test-domain/test-archive.zip'
     ) +
     api.override_step_data('[collect] base_unittests', retcode=1)
   )