Reland "Maintain change log file directly on trunk branch in push-to-trunk."

tools/push-to-trunk/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 45 matching lines @@
     self.Git(MakeArgs(["checkout -b", name, branch]))
 
   def GitDeleteBranch(self, name):
     assert name
     self.Git(MakeArgs(["branch -D", name]))
 
   def GitCheckout(self, name):
     assert name
     self.Git(MakeArgs(["checkout -f", name]))
 
+  def GitCheckoutFile(self, name):
+    assert name
+    self.Git(MakeArgs(["checkout --", name]))
+
   @Strip
   def GitCurrentBranch(self):
     for line in self.Git("status -s -b -uno").strip().splitlines():
       match = re.match(r"^## (.+)", line)
       if match: return match.group(1)
     raise Exception("Couldn't find curent branch.")  # pragma: no cover
 
   @Strip
   def GitLog(self, n=0, format="", grep="", git_hash="", parent_hash="",
              branch="", reverse=False):
@@ skipping 78 matching lines @@
   @Strip
   def GitSVNFindSVNRev(self, git_hash, branch=""):
     return self.Git(MakeArgs(["svn find-rev", git_hash, branch]))
 
   def GitSVNDCommit(self):
     return self.Git("svn dcommit 2>&1", retry_on=lambda x: x is None)
 
   def GitSVNTag(self, version):
     self.Git(("svn tag %s -m \"Tagging version %s\"" % (version, version)),
              retry_on=lambda x: x is None)