Make auto_roll run with a pure git checkout.

tools/push-to-trunk/common_includes.py

 #!/usr/bin/env python
 # Copyright 2013 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 453 matching lines @@
       print "> ",
       answer = self.ReadLine()
 
   # Takes a file containing the patch to apply as first argument.
   def ApplyPatch(self, patch_file, revert=False):
     try:
       self.GitApplyPatch(patch_file, revert)
     except GitFailedException:
       self.WaitForResolvingConflicts(patch_file)
 
-  def FindLastTrunkPush(self, parent_hash="", include_patches=False):
+  def FindLastTrunkPush(
+      self, parent_hash="", branch="", include_patches=False):
     push_pattern = "^Version [[:digit:]]*\.[[:digit:]]*\.[[:digit:]]*"
     if not include_patches:
       # Non-patched versions only have three numbers followed by the "(based
       # on...) comment."
       push_pattern += " (based"
-    branch = "" if parent_hash else "svn/trunk"
+    branch = "" if parent_hash else branch or "svn/trunk"
     return self.GitLog(n=1, format="%H", grep=push_pattern,
                        parent_hash=parent_hash, branch=branch)
 
   def ArrayToVersion(self, prefix):
     return ".".join([self[prefix + "major"],
                      self[prefix + "minor"],
                      self[prefix + "build"],
                      self[prefix + "patch"]])
 
   def SetVersion(self, version_file, prefix):
@@ skipping 162 matching lines @@
     for (number, step_class) in enumerate(step_classes):
       steps.append(MakeStep(step_class, number, self._state, self._config,
                             options, self._side_effect_handler))
     for step in steps[options.step:]:
       if step.Run():
         return 1
     return 0
 
   def Run(self, args=None):
     return self.RunSteps(self._Steps(), args)