// simple interface to wrap our two implementations.
  interface ExecutionListWrapper {
    void add(Runnable runnable, Executor executor);

    void execute();
    /** Returns the underlying implementation, useful for the Footprint benchmark. */
    Object getImpl();
  }

  enum Impl {
    NEW {
      @Override
      ExecutionListWrapper newExecutionList() {

  // simple interface to wrap our two implementations.
  interface ExecutionListWrapper {
    void add(Runnable runnable, Executor executor);

    void execute();
    /** Returns the underlying implementation, useful for the Footprint benchmark. */
    Object getImpl();
  }

  enum Impl {
    NEW {
      @Override
      ExecutionListWrapper newExecutionList() {