Enable Oilpan by default in modules/filesystem/

R=haraken@chromium.org,tzik@chromium.org,tkent@chromium.org
BUG=340522

Review URL: https://codereview.chromium.org/314333002

git-svn-id: svn://svn.chromium.org/blink/trunk@175867 bbb929c8-8fbe-4397-9dbb-9b2b20218538