Refactor the way that git executables are launched in depot tools.

git-cache

Index: git-cache
diff --git a/git-cache b/git-cache
index 14ffa60b9e14ffc0146a23a2a55fd72b7a158995..586ad02208f975ccd7f3ff99e62d4928f1ddb4c0 100755
--- a/git-cache
+++ b/git-cache
@@ -1,26 +1,8 @@
-#!/bin/sh
+#!/bin/bash
 # 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.
 
-# git-cache -- a git-command for managing local caches of remote repositories.
+# git_cache.py - a git-command for managing local caches of remote repositories.
 
-# Test if this script is running under a MSys install.  If it is, we will
-# hardcode the path to Python where possible.
-OUTPUT="$(uname | grep 'MINGW')"
-MINGW=$?
-
-if [ $MINGW = 0 ]; then
-  base_dir="${0%\\*}"
-else
-  base_dir=$(dirname "$0")
-fi
-
-# Uncomment this line if you never use gclient.
-# "$base_dir"/update_depot_tools
-
-if [ -e "$base_dir/python.bat" -a $MINGW = 0 ]; then
-  PYTHONDONTWRITEBYTECODE=1 cmd.exe //c "$base_dir\\python.bat" "$base_dir\\git_cache.py" "$@"
-else
-  PYTHONDONTWRITEBYTECODE=1 exec "$base_dir/git_cache.py" "$@"
-fi
+. $(type -P python_git_runner.sh)