Use the crrev recipe module to fetch commit hashes.

scripts/slave/recipes/bisect.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 base64
 import collections
 import json
 
 DEPS = [
     'auto_bisect',
@@ skipping 240 matching lines @@
   min_rev = range_data[0]['hash']
   max_rev = range_data[-1]['hash']
   output = [[r['hash'], 'ignored'] for r in range_data[1:-1]]
   step_name = ('Expanding revision range.for revisions %s:%s' %
                (min_rev, max_rev))
   return api.step_data(step_name, stdout=api.json.output(output))
 
 
 def _get_step_data_for_revision(api, revision_data, skip_results=False):
   """Generator that produces step patches for fake results."""
-  commit_pos = revision_data['commit_pos']
+  commit_pos_number = revision_data['commit_pos']
   commit_hash = revision_data['hash']
   test_results = revision_data['test_results']
 
   if 'refrange' in revision_data:
     parent_step = 'Resolving reference range.'
-    step_name = parent_step + 'resolving commit_pos ' + commit_pos
-    yield api.step_data(step_name, stdout=api.raw_io.output('hash:' +
-                                                            commit_hash))
+    commit_pos = 'refs/heads/master@{#%s}' % commit_pos_number

[RobertoCN, 2016/03/11 18:40:23]

Question: what's the difference between this string templating and
commit_postion.construct() used in bisector.py?

[qyearsley, 2016/03/11 18:57:50]

There shouldn't be any difference -- and I think it's probably better to use
commit_position.construct. Will upload another patch to do this.

[qyearsley, 2016/03/11 20:07:02]

  File ".../recipes/bisect.py", line 268, in _get_step_data_for_revision
    commit_pos = api.m.commit_position.construct(
AttributeError: 'RecipeTestApi' object has no attribute 'construct'

I'm not sure what's wrong here :-/

Maybe the original way is good anyway, since it's more explicit?

+    step_name = parent_step + 'crrev get commit hash for ' + commit_pos
+    yield api.step_data(
+        step_name,
+        stdout=api.json.output({'git_sha': commit_hash}))
 
   if not skip_results:
     step_name = ('Waiting for chromium@%s.gsutil '
                  'Get test results for build %s') % (commit_hash[:10],
                                                      commit_hash)
     if 'refrange' in revision_data:
       parent_step = 'Gathering reference values.'
     else:
       parent_step = 'Working on revision %s.' % ('chromium@' + commit_hash[:10])
       yield _get_post_bisect_step_data(api, parent_step)
     step_name = parent_step + step_name
     yield api.step_data(step_name, stdout=api.raw_io.output(json.dumps(
         test_results)))
 
     if 'cl_info' in revision_data:
       step_name = 'Reading culprit cl information.'
       stdout = api.json.output(revision_data['cl_info'])
       yield api.step_data(step_name, stdout=stdout)
 
 
 def _get_post_bisect_step_data(api, parent_step=''):
   """Gets step data for perf_dashboard/resource/post_json.py."""
   response = {'status_code': 200}
   return api.step_data(parent_step + 'Post bisect results',
                        stdout=api.json.output(response))