String toPendingString() {
      return callable.toString();
    }
  }

  @WeakOuter
  private final class TrustedFutureInterruptibleAsyncTask
      extends InterruptibleTask<ListenableFuture<V>> {
    private final AsyncCallable<V> callable;

    TrustedFutureInterruptibleAsyncTask(AsyncCallable<V> callable) {
      this.callable = checkNotNull(callable);
    }

    @Override
    final boolean isDone() {