Pass mb_mastername and mb_buildername as parameters to override the default.

scripts/slave/recipes/chromium_gn.py

 # Copyright 2014 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 recipe_engine.types import freeze
 
 DEPS = [
   'bot_update',
   'chromium',
   'chromium_tests',
@@ skipping 170 matching lines @@
 
 
 def all_compile_targets(api, tests):
   """Returns the compile_targets for all the Tests in |tests|."""
   return sorted(set(x
                     for test in tests
                     for x in test.compile_targets(api)))
 
 
 def _RunStepsInternal(api):
-  mastername = api.properties.get('mastername')
-  buildername = api.properties.get('buildername')
+  mastername = api.properties['mastername']
+  buildername = api.properties['buildername']
   bot_config = BUILDERS[mastername]['builders'][buildername]
   is_android = ('Android' in buildername or 'android' in buildername)
   force_clobber = bot_config.get('force_clobber', False)
 
   api.chromium.configure_bot(BUILDERS, ['mb'])
   bot_update_step = api.bot_update.ensure_checkout(
       force=True, patch_root=bot_config.get('root_override'))
 
   # because the 'mb' config is applied, we skip running gyp in the
   # the runhooks step.
@@ skipping 21 matching lines @@
   if api.tryserver.is_tryserver:
     affected_files = api.tryserver.get_files_affected_by_patch()
 
     test_targets = all_compile_targets(api, tests)
 
     test_targets, compile_targets = \
         api.chromium_tests.analyze(
             affected_files,
             test_targets,
             additional_compile_targets,
-            'trybot_analyze_config.json')
+            'trybot_analyze_config.json',
+            mastername,
+            buildername)
     if compile_targets:
       api.chromium.run_mb(mastername, buildername, use_goma=True)
       api.chromium.compile(compile_targets,
                            force_clobber=force_clobber)
     tests = tests_in_compile_targets(api, test_targets, tests)
   else:
     api.chromium.run_mb(mastername, buildername, use_goma=True)
     api.chromium.compile(all_compile_targets(api, tests) +
                          additional_compile_targets,
                          force_clobber=force_clobber)
 
   if tests:
     if api.tryserver.is_tryserver:
       api.chromium_tests.run_tests_on_tryserver(
-          mastername, api, tests, bot_update_step, affected_files)
+          mastername, api, tests, bot_update_step, affected_files,
+          mb_mastername=mastername, mb_buildername=buildername)
     else:
       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):
         test_runner()
 
 
 def RunSteps(api):
   with api.tryserver.set_failure_hash():
@@ skipping 69 matching lines @@
            'gtest_tests': ['base_unittests'],
         }})) +
     api.override_step_data(
         'analyze',
         api.json.output({
           'status': 'Found dependency',
           'test_targets': ['net_unittests'],
           'compile_targets': ['net_unittests'],
         }))
   )