Added virtualenv for depot_tools

update_depot_tools.bat

 @echo off
 :: 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 batch file will try to sync the root directory.
 
 setlocal
 
 :: Windows freaks out if a file is overwritten while it's being executed.  Copy
 :: this script off to a temporary location and reinvoke from there before
 :: running any svn or git commands.
 IF %~nx0==update_depot_tools.bat (
   COPY /Y %~dp0update_depot_tools.bat %TEMP%\update_depot_tools_tmp.bat >nul
   if errorlevel 1 goto :EOF
   %TEMP%\update_depot_tools_tmp.bat %~dp0 %*
 )
 
 set DEPOT_TOOLS_DIR=%1
 SHIFT
 
 set GIT_URL=https://chromium.googlesource.com/chromium/tools/depot_tools.git
 
 :: Will download git, svn and python.
 call "%DEPOT_TOOLS_DIR%bootstrap\win\win_tools.bat"
 if errorlevel 1 goto :EOF
 :: Now clear errorlevel so it can be set by other programs later.
 set errorlevel=
 
+:: Initialize/update virtualenv.
+cd "%DEPOT_TOOLS_DIR%"
+python -u bootstrap\bootstrap.py --deps_file bootstrap\deps.pyl ENV
+if errorlevel 1 goto :EOF
+
 :: Shall skip automatic update?
 IF "%DEPOT_TOOLS_UPDATE%" == "0" GOTO :EOF
 
 :: We need either .\.svn\. or .\.git\. to be able to sync.
 IF EXIST "%DEPOT_TOOLS_DIR%.svn\." GOTO :SVN_UPDATE
 IF EXIST "%DEPOT_TOOLS_DIR%.git\." GOTO :GIT_UPDATE
 echo Error updating depot_tools, no revision tool found.
 goto :EOF
 
 
@@ skipping 23 matching lines @@
 call git fetch -q origin > NUL
 call git rebase -q origin/master > NUL
 if errorlevel 1 echo Failed to update depot_tools.
 goto :EOF
 
 
 :GIT_SVN_UPDATE
 cd /d "%DEPOT_TOOLS_DIR%."
 call git svn rebase -q -q
 goto :EOF