Enable implicit auto-upgrade to python 2.7.5.

bootstrap/win/win_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 script will try to find if svn and python are accessible and it not,
 :: it will try to download it and 'install' it in depot_tools.
 
 :: Sadly, we can't use SETLOCAL here otherwise it ERRORLEVEL is not correctly
 :: returned.
@@ skipping 95 matching lines @@
 :SVN_FAIL
 echo ... Failed to checkout svn automatically.
 echo Please visit http://subversion.tigris.org to download the latest subversion client
 echo before continuing.
 echo You can also get the "prebacked" version used at %WIN_TOOLS_ROOT_URL%/third_party/
 set ERRORLEVEL=1
 goto :END
 
 
 :PYTHON_CHECK
-if "%DEPOT_TOOLS_PYTHON_275%" == "1" goto :PY275_CHECK
-goto :PY26_CHECK
+if "%DEPOT_TOOLS_PYTHON_275%" == "0" goto :PY26_CHECK
+goto :PY275_CHECK
 
 
 :PY26_CHECK
 if not exist "%WIN_TOOLS_ROOT_DIR%\python_bin" goto :PY26_INSTALL
 if not exist "%WIN_TOOLS_ROOT_DIR%\python.bat" goto :PY26_INSTALL
 set ERRORLEVEL=0
 goto :END
 
 
 :PY275_CHECK
@@ skipping 42 matching lines @@
 goto :END
 
 
 :returncode
 set WIN_TOOLS_ROOT_URL=
 set WIN_TOOLS_ROOT_DIR=
 exit /b %ERRORLEVEL%
 
 :END
 call :returncode %ERRORLEVEL%