Execute the script using python api module.

scripts/slave/recipe_modules/auto_bisect/api.py

 # Copyright 2015 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.
 
 """API for the bisect recipe module.
 
 This API is meant to enable the bisect recipe to bisect any chromium-supported
 platform for any test that can be run via buildbot, perf or otherwise.
 """
 
@@ skipping 92 matching lines @@
   def run_bisect_script(self, extra_src='', path_to_config='', **kwargs):
     """Executes run-perf-bisect-regression.py to perform bisection.
 
     Args:
       extra_src (str): Path to extra source file. If this is supplied,
         bisect script will use this to override default behavior.
       path_to_config (str): Path to the config file to use. If this is supplied,
         the bisect script will use this to override the default config file
         path.
     """
-    self.m.step(
+    self.m.python(
         'Preparing for Bisection',
-        [self.m.path['checkout'].join('tools',
-                                      'prepare-bisect-perf-regression.py'),
-        '-w', self.m.path['slave_build']])
+        script=self.m.path['checkout'].join(
+            'tools', 'prepare-bisect-perf-regression.py'),
+        args=['-w', self.m.path['slave_build']])
     args = []
 
     kwargs['allow_subannotations'] = True
 
     if extra_src:
       args = args + ['--extra_src', extra_src]
     if path_to_config:
       args = args + ['--path_to_config', path_to_config]
 
     if self.m.chromium.c.TARGET_PLATFORM != 'android':
       args += ['--path_to_goma', self.m.path['build'].join('goma')]
     args += [
         '--build-properties',
          self.m.json.dumps(dict(self.m.properties.legacy())),
       ]
     self.m.chromium.runtest(
         self.m.path['checkout'].join('tools', 'run-bisect-perf-regression.py'),
         ['-w', self.m.path['slave_build']] + args,
         name='Running Bisection',
         xvfb=True, **kwargs)