code: public void loadDimensionIterable(
        Iterable<String> oldDimensionOrder,
        Map<String, ColumnCapabilitiesImpl> oldColumnCapabilities
    )
    {
      synchronized (dimensionDescs) {
        if (!dimensionDescs.isEmpty()) {
          throw new ISE("Cannot load dimension order when existing order[%s] is not empty.", dimensionDescs.keySet());
        }
        for (String dim : oldDimensionOrder) {
          if (dimensionDescs.get(dim) == null) {
            ColumnCapabilitiesImpl capabilities = oldColumnCapabilities.get(dim);
            columnCapabilities.put(dim, capabilities);
            DimensionHandler handler = DimensionHandlerUtils.getHandlerFromCapabilities(dim, capabilities, null);
            addNewDimension(dim, capabilities, handler);
          }
        }
      }
    }
docs: Currently called to initialize IncrementalIndex dimension order during index creation
  Index dimension ordering could be changed to initialize from DimensionsSpec after resolution of
  https://github.com/apache/incubator-druid/issues/2011