Add tag write access to merge script.

tools/push-to-trunk/auto_tag.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 sys
 
 from common_includes import *
 
@@ skipping 135 matching lines @@
     print "Tagging revision %s with %s" % (lkgr_svn, self["candidate_version"])
 
 
 class MakeTag(Step):
   MESSAGE = "Tag the version."
 
   def RunStep(self):
     if not self._options.dry_run:
       self.GitReset(self["lkgr"])
       # FIXME(machenbach): Make this work with the git repo.
-      self.vc.Tag(self["candidate_version"], "svn/bleeding_edge")
+      self.vc.Tag(self["candidate_version"],
+                  "svn/bleeding_edge",
+                  "This won't work!")
 
 
 class CleanUp(Step):
   MESSAGE = "Clean up."
 
   def RunStep(self):
     self.CommonCleanup()
 
 
 class AutoTag(ScriptsBase):
@@ skipping 23 matching lines @@
       GetOldestUntaggedVersion,
       GetLKGRs,
       CalculateTagRevision,
       MakeTag,
       CleanUp,
     ]
 
 
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(AutoTag().Run())