Revert of Use the crrev recipe module to fetch commit hashes.

scripts/slave/recipe_modules/auto_bisect/bisector.py

Index: scripts/slave/recipe_modules/auto_bisect/bisector.py
diff --git a/scripts/slave/recipe_modules/auto_bisect/bisector.py b/scripts/slave/recipe_modules/auto_bisect/bisector.py
index 14a6dd7587700d64fd2f3a3292dae7d1b9108b5f..34bce59c9899cf08a8863c06d36f69d7bf015579 100644
--- a/scripts/slave/recipe_modules/auto_bisect/bisector.py
+++ b/scripts/slave/recipe_modules/auto_bisect/bisector.py
@@ -147,13 +147,7 @@
     if self._is_sha1(rev):  # pragma: no cover
       return rev
     if rev.isdigit():
-      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
+      return self._api.m.commit_position.chromium_hash_from_commit_position(rev)
     self.surface_result('BAD_REV')  # pragma: no cover
     raise self.api.m.step.StepFailure(
         'Invalid input revision: %r' % (rev,))  # pragma: no cover