Fix slash direction: paths in msysgit use /, not \.

update_depot_tools

 #!/usr/bin/env bash
 # Copyright (c) 2012 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 script will try to sync the bootstrap directories and then defer control.
 
 if [ "$USER" == "root" ];
 then
   echo Running depot tools as root is sad.
   exit
 fi
 
 # Test if this script is running under a MSys install.  If it is, we will
 # hardcode the paths to SVN and Git where possible.
 OUTPUT="$(uname | grep 'MINGW')"
 MINGW=$?
 
 if [ $MINGW = 0 ]; then
-  base_dir="${0%\\*}"
+  base_dir="${0%/*}"
 else
   base_dir=$(dirname "$0")
   if [ -L "$base_dir" ]; then
     base_dir=`cd "$base_dir" && pwd -P`
   fi
 fi
 
 # Don't try to use Cygwin tools.  Get real win32 tools using the batch script.
 OUTPUT="$(uname | grep 'CYGWIN')"
 CYGWIN=$?
@@ skipping 119 matching lines @@
       echo "Depot Tools has been updated to revision $AFTER_REVISION." 1>&2
     fi
   fi
 fi
 
 find "$base_dir" -iname "*.pyc" -exec rm {} \;
 
 # Initialize/update virtualenv.
 cd $base_dir
 python -u ./bootstrap/bootstrap.py --deps_file bootstrap/deps.pyl --quiet ENV