Store hashes of current and previous shipped V8 version

tools/release/git_recipes.py

 #!/usr/bin/env python
 # Copyright 2014 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
@@ skipping 262 matching lines @@
         return match.group(2)
 
     # Extract the svn revision from 'git-svn' metadata
     value = footer_map.get(GIT_SVN_ID_FOOTER_KEY)
     if value:
       match = GIT_SVN_ID_RE.match(value)
       if match:
         return match.group(1)
     raise GitFailedException("Couldn't determine commit position for %s" %
                              git_hash)
+
+  def GitGetHashOfTag(self, tag_name, **kwargs):
+    return self.Git("rev-list -1 " + tag_name).strip().encode("ascii", "ignore")