Add a git-drover.

git_common.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Monkeypatch IMapIterator so that Ctrl-C can kill everything properly.
 # Derived from https://gist.github.com/aljungberg/626518
 import multiprocessing.pool
 from multiprocessing.pool import IMapIterator
 def wrapper(func):
   def wrap(self, timeout=None):
     return func(self, timeout=timeout or 1e100)
   return wrap
 IMapIterator.next = wrapper(IMapIterator.next)
 IMapIterator.__next__ = IMapIterator.next
 # TODO(iannucci): Monkeypatch all other 'wait' methods too.
 
 
 import binascii
 import collections
 import contextlib
 import functools
 import logging
 import os
 import re
+import shutil
 import signal
 import sys
 import tempfile
 import textwrap
 import threading
 
 import subprocess2
 
 ROOT = os.path.abspath(os.path.dirname(__file__))
 
@@ skipping 775 matching lines @@
         hash=branch_hash, upstream=upstream_branch, ahead=ahead, behind=behind)
 
   # Set None for upstreams which are not branches (e.g empty upstream, remotes
   # and deleted upstream branches).
   missing_upstreams = {}
   for info in info_map.values():
     if info.upstream not in info_map and info.upstream not in missing_upstreams:
       missing_upstreams[info.upstream] = None
 
   return dict(info_map.items() + missing_upstreams.items())
+
+
+def make_workdir_common(repository, new_workdir, files_to_symlink,
+                        files_to_copy):
+  os.makedirs(new_workdir)
+  for entry in files_to_symlink:
+    clone_file(repository, new_workdir, entry, os.symlink)
+  for entry in files_to_copy:
+    clone_file(repository, new_workdir, entry, shutil.copy)
+
+
+def make_workdir(repository, new_workdir):
+  GIT_DIRECTORY_WHITELIST = [
+    'config',
+    'info',
+    'hooks',
+    'logs/refs',
+    'objects',
+    'packed-refs',
+    'refs',
+    'remotes',
+    'rr-cache',
+    'svn'
+  ]
+  make_workdir_common(repository, new_workdir, GIT_DIRECTORY_WHITELIST,
+                      ['HEAD'])
+
+
+def clone_file(repository, new_workdir, link, operation):
+  if not os.path.exists(os.path.join(repository, link)):
+    return
+  link_dir = os.path.dirname(os.path.join(new_workdir, link))
+  if not os.path.exists(link_dir):
+    os.makedirs(link_dir)
+  operation(os.path.join(repository, link), os.path.join(new_workdir, link))