auto_bisect: fix path for checking DEPS

scripts/slave/recipe_modules/auto_bisect/revision_state.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.
 
 """An interface for holding state and result of revisions in a bisect job.
 
 When implementing support for tests other than perf, one should extend this
 class so that the bisect module and recipe can use it.
 
 See perf_revision_state for an example.
@@ skipping 138 matching lines @@
       self._do_test()
       self.status = RevisionState.TESTING
 
   def deps_change(self):
     """Uses `git show` to see if a given commit contains a DEPS change."""
     # Avoid checking DEPS changes for dependency repo revisions.
     # crbug.com/580681
     if self.needs_patch:  # pragma: no cover
       return False
     api = self.bisector.api
-    cwd = api.m.path['slave_build'].join(
+    working_dir = api.working_dir or api.m.path['slave_build']
+    cwd = working_dir.join(
         depot_config.DEPOT_DEPS_NAME[self.depot_name]['src'])
     name = 'Checking DEPS for ' + self.commit_hash
     step_result = api.m.git(
         'show', '--name-only', '--pretty=format:',
         self.commit_hash, cwd=cwd, stdout=api.m.raw_io.output(), name=name)
     if self.bisector.dummy_builds and not self.commit_hash.startswith('dcdc'):
       return False
     if 'DEPS' in step_result.stdout.splitlines():  # pragma: no cover
       return True
     return False  # pragma: no cover
@@ skipping 417 matching lines @@
     else:
       next_revision_to_test.retest()
 
   def __repr__(self):
     if self.overall_return_code is not None:
       return ('RevisionState(rev=%s, values=%r, overall_return_code=%r, '
               'std_dev=%r)') % (self.revision_string(), self.values,
                                 self.overall_return_code, self.std_dev)
     return ('RevisionState(rev=%s, values=%r, mean_value=%r, std_dev=%r)' % (
         self.revision_string(), self.values, self.mean_value, self.std_dev))