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

git-number

Index: git-number
diff --git a/git-number b/git-number
index 6c06f055de9e284026ea8d8485627d76bd832478..c311df90f2dcef8aab91af639b6f4b2f4059dc82 100755
--- a/git-number
+++ b/git-number
@@ -1,27 +1,9 @@
-#!/bin/sh
+#!/bin/bash
 # Copyright 2013 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-number -- a git-command for calculating and displaying the generation
+# git_number.py - a git-command for calculating and displaying the generation
 # number of a commit.
 
-# 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" "$base_dir\\git_number.py" "$@"
-else
-  PYTHONDONTWRITEBYTECODE=1 exec "$base_dir/git_number.py" "$@"
-fi
+. $(type -P python_git_runner.sh)