class Opal::Context

#setup_v8
then the v8 context will de removed. It can be reset by calling
the opal runtime to do it's at_exit() calls (if applicable) and
Finishes the context, i.e. tidy everything up. This will cause

def finish
  return unless @v8
  eval "opal.runtime.do_at_exit()", "(opal)"
  @v8 = nil
end