final Queue<IndexedIterator<T>> queue;

    MergingIterator(
        Iterable<? extends Iterator<? extends T>> iterators, Comparator<? super T> itemComparator) {
      // A comparator that's used by the heap, allowing the heap
      // to be sorted based on the top of each iterator, with insertion order as tiebreaker
      Comparator<IndexedIterator<T>> heapComparator =
          (o1, o2) ->
              ComparisonChain.start()