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

scripts/slave/recipe_modules/chromium/api.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 re
 
 from recipe_engine import recipe_api
 from recipe_engine import util as recipe_util
 
 from . import builders
@@ skipping 562 matching lines @@
         name='gn',
         script=self.m.path['depot_tools'].join('gn.py'),
         args=[
             '--root=%s' % str(self.m.path['checkout']),
             'gen',
             build_dir,
             '--args=%s' % ' '.join(gn_args),
         ])
 
   def run_mb(self, mastername, buildername, use_goma=True,
-             mb_config_path=None):
+             mb_config_path=None, swarming_targets=None):
     mb_config_path = (mb_config_path or
                       self.m.path['checkout'].join('tools', 'mb',
                                                    'mb_config.pyl'))
+    swarming_targets = swarming_targets or []
+
     args=[
         'gen', '-v',
         '-m', mastername,
         '-b', buildername,
         '--config-file', mb_config_path,
     ]
+
     if use_goma:
-        args += [
-            '--goma-dir', self.m.path['build'].join('goma'),
-        ]
-    args += [
-        '//out/%s' % self.c.build_config_fs
-    ]
+      args += ['--goma-dir', self.m.path['build'].join('goma')]
+
+    if swarming_targets:
+      data = '\n'.join(swarming_targets) + '\n'
+      args += ['--swarming-targets-file', self.m.raw_io.input(data)]
+
+    args += ['//out/%s' % self.c.build_config_fs]
 
     # This runs with no env being passed along, so we get a clean environment
     # without any GYP_DEFINES being present to cause confusion.
     self.m.python(name='generate_build_files',
                   script=self.m.path['checkout'].join('tools', 'mb', 'mb.py'),
                   args=args)
 
   def taskkill(self):
     self.m.python(
       'taskkill',
@@ skipping 153 matching lines @@
             '--output', self.m.json.output(),
             '--',
         ] + self.get_common_args_for_scripts(),
         step_test_data=lambda: self.m.json.test_api.output({}))
 
   def download_lto_plugin(self):
     return self.m.python(
         name='download LTO plugin',
         script=self.m.path['checkout'].join(
             'build', 'download_gold_plugin.py'))