presto-main/src/main/java/io/prestosql/operator/WindowInfo.java/DriverWindowInfoBuilder/addIndex
class DriverWindowInfoBuilder:        public void addIndex(PagesIndex index)
        {
            if (currentIndexInfoBuilder != null) {
                Optional<IndexInfo> indexInfo = currentIndexInfoBuilder.build();
                indexInfo.ifPresent(indexInfosBuilder::add);
            }
            currentIndexInfoBuilder = new IndexInfoBuilder(index.getPositionCount(), index.getEstimatedSize().toBytes());
        }