Re-land: Added virtualenv for depot_tools

update_depot_tools.bat

Index: update_depot_tools.bat
diff --git a/update_depot_tools.bat b/update_depot_tools.bat
index 33fa40b220e8755ec693c924dc135e8a0e7be6c0..2b0f1cba70ccd93f6167df2b7679af89a04bf2f4 100644
--- a/update_depot_tools.bat
+++ b/update_depot_tools.bat
@@ -27,6 +27,23 @@ if errorlevel 1 goto :EOF
 :: Now clear errorlevel so it can be set by other programs later.
 set errorlevel=
 
+:: Initialize/update virtualenv.
+set VIRTUALENV_REPO=https://chromium.googlesource.com/infra/third_party/virtualenv.git
+set VIRTUALENV_REVISION=4243b272823228dde5d18a7400c404ce52fb4cea
+cd /d "%DEPOT_TOOLS_DIR%."
+IF NOT EXIST "bootstrap\virtualenv" (
+  echo Fetching virtualenv from %VIRTUALENV_REPO%@%VIRTUALENV_REVISION%
+  call git clone %VIRTUALENV_REPO% "bootstrap\virtualenv" --no-checkout --quiet
+  if errorlevel 1 goto :EOF
+  cd "bootstrap\virtualenv\."
+  call git checkout %VIRTUALENV_REVISION% --quiet
+  if errorlevel 1 goto :EOF
+  cd ..\.. 
+  echo Done fetching virtualenv
+)
+python -u bootstrap\bootstrap.py --deps_file bootstrap\deps.pyl --quiet ENV
+if errorlevel 1 goto :EOF
+
 :: Shall skip automatic update?
 IF "%DEPOT_TOOLS_UPDATE%" == "0" GOTO :EOF