Drop unwanted dependencies on chromium_tests recipe module

scripts/slave/recipe_modules/webrtc/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.
 
 from recipe_engine.types import freeze
 from recipe_engine import recipe_api
 from . import builders
 from . import steps
 
 
@@ skipping 127 matching lines @@
       self.m.chromium_swarming.configure_swarming(
           'webrtc',
           precommit=self.m.tryserver.is_tryserver,
           mastername=mastername)
       self.m.swarming.set_default_dimension(
           'os',
           self.m.swarming.prefered_os_dimension(
               self.m.platform.name).split('-', 1)[0])
 
   def checkout(self, **kwargs):
-    self._working_dir = self.m.chromium_tests.get_checkout_dir({})
+    self._working_dir = self.m.chromium_checkout.get_checkout_dir({})
     if self._working_dir:
       kwargs.setdefault('cwd', self._working_dir)
 
     update_step = self.m.bot_update.ensure_checkout(**kwargs)
     assert update_step.json.output['did_run']
 
     # Whatever step is run right before this line needs to emit got_revision.
     revs = update_step.presentation.properties
     self.revision = revs['got_revision']
     self.revision_cp = revs['got_revision_cp']
@@ skipping 158 matching lines @@
   def clean_test_output(self):
     """Remove all test output in out/, since we have tests leaking files."""
     out_dir = self.m.path['checkout'].join('out')
     self.m.python('clean test output files',
                   script=self.resource('cleanup_files.py'),
                   args=[out_dir],
                   infra_step=True)
 
   def virtual_webcam_check(self):
     self.m.python('webcam_check', self.resource('ensure_webcam_is_running.py'))