Pass the status of enable_oilpan when generating the blink_gc_plugin flags.

Change to blink_gc_plugin_flags.sh in https://codereview.chromium.org/156243006/

BUG=334149
R=ager@chromium.org

Review URL: https://codereview.chromium.org/148783004

git-svn-id: svn://svn.chromium.org/blink/trunk@166811 bbb929c8-8fbe-4397-9dbb-9b2b20218538