[release-tools] Fix possible race condition in retrieval of latest rolled version

tools/release/auto_roll.py

 #!/usr/bin/env python
 # Copyright 2014 the V8 project 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 argparse
 import json
 import os
 import sys
 import urllib
@@ skipping 30 matching lines @@
 class DetectLastRoll(Step):
   MESSAGE = "Detect commit ID of the last Chromium roll."
 
   def RunStep(self):
     # The revision that should be rolled. Check for the latest of the most
     # recent releases based on commit timestamp.
     revisions = self.GetRecentReleases(
         max_age=self._options.max_age * DAY_IN_SECONDS)
     assert revisions, "Didn't find any recent release."
 
+    # Update Chromium checkout before DEPS check to fix possible race-condition
+    self.GitPull(cwd=self._options.chromium)
+
     # Interpret the DEPS file to retrieve the v8 revision.
     # TODO(machenbach): This should be part or the roll-deps api of
     # depot_tools.
     Var = lambda var: '%s'
     exec(FileToText(os.path.join(self._options.chromium, "DEPS")))
 
     # The revision rolled last.
     self["last_roll"] = vars['v8_revision']
     last_version = self.GetVersionTag(self["last_roll"])
     assert last_version, "The last rolled v8 revision is not tagged."
@@ skipping 65 matching lines @@
   def _Steps(self):
     return [
       CheckActiveRoll,
       DetectLastRoll,
       RollChromium,
     ]
 
 
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(AutoRoll().Run())