Enable installing git by default on Windows.

BUG=79356
Review URL: http://codereview.chromium.org/8369019

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@107206 0039d316-1c4b-4281-b951-d872f2087c98

bootstrap/win/win_tools.bat

@@ -25,8 +25,9 @@ if "%1" == "force" (
 :GIT_CHECK
 :: If the batch file exists, skip the git check.
 if exist "%WIN_TOOLS_ROOT_DIR%\git.bat" goto :SVN_CHECK
-if "%GIT_TOOLS_FORCE%" == "1" goto :GIT_INSTALL
-:: The normal initialization will happen here when we're ready to deploy.
+if "%WIN_TOOLS_FORCE%" == "1" goto :GIT_INSTALL
+call git --version 2>nul 1>nul
+if errorlevel 1 goto :GIT_INSTALL
 goto :SVN_CHECK