Don't reinstall *every* time. Just if the batch file doesn't exist.

bootstrap/win/win_tools.bat

 @echo off
 :: Copyright (c) 2009 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.
 
 set WIN_TOOLS_ROOT_URL=http://src.chromium.org/svn/trunk/tools
 set WIN_TOOLS_ROOT_DIR=%~dp0..\..
 
 if "%1" == "force" (
   set WIN_TOOLS_FORCE=1
   shift /1
 )
 
 :SVN_CHECK
 :: If the batch file exists, skip the svn check.
-if "%WIN_TOOLS_FORCE%" == "1" goto :SVN_INSTALL
 if exist "%WIN_TOOLS_ROOT_DIR%\svn.bat" goto :PYTHON_CHECK
+if "%WIN_TOOLS_FORCE%" == "1" goto :SVN_FORCE

[sigurdur.asgeirsson_gmail.com, 2009/05/07 14:38:25]

Won't this skip the SVN install if svn is present, even when force is specified?

 call svn --version 2>nul 1>nul
 if errorlevel 1 goto :SVN_INSTALL
 goto :PYTHON_CHECK
 
 
 :SVN_INSTALL
 echo Installing subversion ...
 :: svn is not accessible; check it out and create 'proxy' files.
 if exist "%~dp0svn.7z" del "%~dp0svn.7z"
 cscript //nologo //e:jscript "%~dp0get_file.js" %WIN_TOOLS_ROOT_URL%/third_party/svn_win_client.zip "%~dp0svn.zip"
@@ skipping 13 matching lines @@
 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 the batch file exists, skip the python check.
-if "%WIN_TOOLS_FORCE%" == "1" goto :PYTHON_INSTALL
 set ERRORLEVEL=0
 if exist "%WIN_TOOLS_ROOT_DIR%\python.bat" goto :END
+if "%WIN_TOOLS_FORCE%" == "1" goto :PYTHON_INSTALL

[sigurdur.asgeirsson_gmail.com, 2009/05/07 14:38:25]

ditto?

 call python --version 2>nul 1>nul
 if errorlevel 1 goto :PYTHON_INSTALL
 
 :: We are done.
 set ERRORLEVEL=0
 goto :END
 
 
 :PYTHON_INSTALL
 echo Installing python ...
@@ skipping 16 matching lines @@
 goto :END
 
 
 :returncode
 set WIN_TOOLS_ROOT_URL=
 set WIN_TOOLS_ROOT_DIR=
 exit /b %ERRORLEVEL%
 
 :END
 call :returncode %ERRORLEVEL%