Make git version numbers external to batch script.

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 determine if python, git, or svn binaries need updates.  It
 :: returns 123 if the user's shell must restart, otherwise !0 is failure
 
 :: Sadly, we can't use SETLOCAL here otherwise it ERRORLEVEL is not correctly
 :: returned.
@@ skipping 50 matching lines @@
 
 :: must explicitly use FIND_EXE to prevent this from grabbing e.g. gnuwin32 or
 :: msys versions.
 set FIND_EXE=%SYSTEMROOT%\System32\find.exe
 
 :: Check to see if we're on a 32 or 64 bit system
 :: (parens) are necessary, otherwise batch puts an extra space after 32.
 reg Query "HKLM\Hardware\Description\System\CentralProcessor\0" | %FIND_EXE% /i "x86" > NUL && (set OS_BITS=32) || (set OS_BITS=64)
 
 if not exist "%WIN_TOOLS_ROOT_DIR%\.git_bleeding_edge" (
-  set GIT_VERSION=2.8.3
+  set /p GIT_VERSION= <"%~dp0git_version.txt"
 ) else (
-  set GIT_VERSION=2.8.3
+  set /p GIT_VERSION= <"%~dp0git_version_bleeding_edge.txt"
 )
 set GIT_VERSION=%GIT_VERSION%-%OS_BITS%
 
 set GIT_FETCH_URL=%CHROME_INFRA_URL%PortableGit-%GIT_VERSION%-bit.7z.exe
 set GIT_DOWNLOAD_PATH=%ZIP_DIR%\git.7z.exe
 set GIT_BIN_DIR=git-%GIT_VERSION%_bin
 set GIT_INST_DIR=%WIN_TOOLS_ROOT_DIR%\%GIT_BIN_DIR%
 set GIT_EXE_PATH=%GIT_INST_DIR%\bin\git.exe
 
 :: Clean up any release which doesn't match the one we want.
@@ skipping 132 matching lines @@
 set ERRORLEVEL=1
 goto :END
 
 
 :returncode
 set WIN_TOOLS_ROOT_DIR=
 exit /b %ERRORLEVEL%
 
 :END
 call :returncode %ERRORLEVEL%