Make msys depot_tools upgrade process smoother.

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 [ "$USER" == "root" ];
 then
   echo Running depot tools as root is sad.
@@ skipping 24 matching lines @@
 else
   base_dir=$(dirname "$0")
   if [ -L "$base_dir" ]; then
     base_dir=`cd "$base_dir" && pwd -P`
   fi
 fi
 
 # We want to update the bundled tools even under MinGW.
 if [ $MINGW = 0 ]; then
   $COMSPEC /c `cygpath -w "$base_dir/bootstrap/win/win_tools.bat"`
+  case $? in
+    123)
+      # msys environment was upgraded, need to quit.
+      exit 123
+      ;;
+    0)
+      ;;
+    *)
+      exit $?
+  esac
 fi
 
 CANONICAL_GIT_URL="https://chromium.googlesource.com/chromium/tools/depot_tools.git"
 
 SVN="svn"
 if [ -d "$base_dir/svn_bin" -a $MINGW = 0 ]; then
   SVN="$base_dir/svn_bin/svn.exe"
 fi
 
 GIT="git"
@@ skipping 103 matching lines @@
   "$SVN" -q up "$base_dir"
   AFTER_REVISION=$(get_svn_revision)
   if [[ "$BEFORE_REVISION" != "$AFTER_REVISION" ]]; then
     if [ -z "$DEPOT_TOOLS_HIDE_UPDATED_MESSAGE" ]; then
       echo "Depot Tools has been updated to revision $AFTER_REVISION." 1>&2
     fi
   fi
 fi
 
 find "$base_dir" -iname "*.pyc" -exec rm -f {} \;