Revert of Removed virtualenv from depot_tools

bootstrap/virtualenv/virtualenv_embedded/activate.csh

+# This file must be used with "source bin/activate.csh" *from csh*.
+# You cannot run it directly.
+# Created by Davide Di Blasi <davidedb@gmail.com>.
+
+alias deactivate 'test $?_OLD_VIRTUAL_PATH != 0 && setenv PATH "$_OLD_VIRTUAL_PATH" && unset _OLD_VIRTUAL_PATH; rehash; test $?_OLD_VIRTUAL_PROMPT != 0 && set prompt="$_OLD_VIRTUAL_PROMPT" && unset _OLD_VIRTUAL_PROMPT; unsetenv VIRTUAL_ENV; test "\!:*" != "nondestructive" && unalias deactivate && unalias pydoc'
+
+# Unset irrelevant variables.
+deactivate nondestructive
+
+setenv VIRTUAL_ENV "__VIRTUAL_ENV__"
+
+set _OLD_VIRTUAL_PATH="$PATH"
+setenv PATH "$VIRTUAL_ENV/__BIN_NAME__:$PATH"
+
+
+
+if ("__VIRTUAL_PROMPT__" != "") then
+    set env_name = "__VIRTUAL_PROMPT__"
+else
+    if (`basename "$VIRTUAL_ENV"` == "__") then
+        # special case for Aspen magic directories
+        # see http://www.zetadev.com/software/aspen/
+        set env_name = `basename \`dirname "$VIRTUAL_ENV"\``
+    else
+        set env_name = `basename "$VIRTUAL_ENV"`
+    endif
+endif
+
+# Could be in a non-interactive environment,
+# in which case, $prompt is undefined and we wouldn't
+# care about the prompt anyway.
+if ( $?prompt ) then
+    set _OLD_VIRTUAL_PROMPT="$prompt"
+    set prompt = "[$env_name] $prompt"
+endif
+
+unset env_name
+
+alias pydoc python -m pydoc
+
+rehash
+