Use the crrev recipe module to fetch commit hashes.

scripts/slave/recipe_modules/auto_bisect/bisector.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.
 
 import json
 import re
 import time
 import urllib
 
 from . import depot_config
@@ skipping 129 matching lines @@
 
     Args:
       rev (str): A commit hash or commit position number.
 
     Returns:
       A 40-digit git commit hash string.
     """
     if self._is_sha1(rev):  # pragma: no cover
       return rev
     if rev.isdigit():
-      return self._api.m.commit_position.chromium_hash_from_commit_position(rev)
+      commit_position = self._api.m.commit_position.construct(
+          branch='refs/heads/master', value=rev)
+      try:
+        return self._api.m.crrev.to_commit_hash(commit_position)
+      except self.api.m.step.StepFailure:  # pragma: no cover
+        self.surface_result('BAD_REV')
+        raise

[qyearsley, 2016/03/07 23:32:53]

Note: this will make up to 3 requests to crrev and if it fails 3 times, then we
conclude that we got a bad input rev.

     self.surface_result('BAD_REV')  # pragma: no cover
     raise self.api.m.step.StepFailure(
         'Invalid input revision: %r' % (rev,))  # pragma: no cover
 
   @staticmethod
   def _is_sha1(s):
     return bool(re.match('^[0-9A-Fa-f]{40}$', s))
 
   def significantly_different(
       self, list_a, list_b,
@@ skipping 687 matching lines @@
         })
     return revision_rows
 
   def _get_build_url(self):
     properties = self.api.m.properties
     bot_url = properties.get('buildbotURL',
                              'http://build.chromium.org/p/chromium/')
     builder_name = urllib.quote(properties.get('buildername', ''))
     builder_number = str(properties.get('buildnumber', ''))
     return '%sbuilders/%s/builds/%s' % (bot_url, builder_name, builder_number)