Add git thaw/freeze to depot_tools.

python_git_runner.sh

 #!/bin/bash
 # Copyright (c) 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.
 
 ## This file is designed to be sourced from a bash script whose name takes the
 ## form 'git-sub-command'. This script will then instead invoke 'git_sub_command.py'
 ## correctly under mingw as well as posix-ey systems, passing along all other
 ## command line flags.
 
 ## Example:
 ## echo ". python_git_runner.sh" > git-foo-command
 ## ./git-foo-command  #=> runs `python git_foo_command.py`
 
 OUTPUT="$(uname | grep 'MINGW')"
 MINGW=$?
 
 BASE="$(basename "$0")"
-SCRIPT="${BASE//-/_}.py"
+SCRIPT="${SCRIPT-${BASE//-/_}.py}"
 
 if [ $MINGW = 0 ]; then
   base_dir="${0%\\*}"
 else
   base_dir=$(dirname "$0")
 fi
 
 if [ -e "$base_dir/python.bat" -a $MINGW = 0 ]; then
   PYTHONDONTWRITEBYTECODE=1 cmd.exe //c "$base_dir\\python.bat" "$base_dir\\$SCRIPT" "$@"
 else
   PYTHONDONTWRITEBYTECODE=1 exec "$base_dir/$SCRIPT" "$@"
 fi