// TODO(fry): Look into Maps.KeySet and Maps.Values, which can ideally be reused here but are
  // currently only package visible.
  abstract class AbstractCacheSet<T> extends AbstractSet<T> {
    final ConcurrentMap<?, ?> map;

    AbstractCacheSet(ConcurrentMap<?, ?> map) {
      this.map = map;
    }

    @Override
    public int size() {
      return map.size();
    }

    @Override