Let release scripts determine version based on tags.

tools/release/chromium_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 os
 import sys
 
 from common_includes import *
 
 
 class Preparation(Step):
   MESSAGE = "Preparation."
 
   def RunStep(self):
     # Update v8 remote tracking branches.
     self.GitFetchOrigin()
 
 
 class DetectLastPush(Step):
-  MESSAGE = "Detect commit ID of last push to candidates."
+  MESSAGE = "Detect commit ID of last release."
 
   def RunStep(self):
-    self["last_push"] = self._options.last_push or self.FindLastCandidatesPush(
-        branch="origin/candidates", include_patches=True)
+    # The revision that should be rolled.
+    self["last_push"] = self._options.last_push or self.GetLatestRelease()
     self["push_title"] = self.GitLog(n=1, format="%s",
                                      git_hash=self["last_push"])
 
 
 class SwitchChromium(Step):
   MESSAGE = "Switch to Chromium checkout."
 
   def RunStep(self):
     self["v8_path"] = os.getcwd()
     cwd = self._options.chromium
@@ skipping 109 matching lines @@
       SwitchChromium,
       UpdateChromiumCheckout,
       UploadCL,
       SwitchV8,
       CleanUp,
     ]
 
 
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(ChromiumRoll().Run())