code: public C getCell(int itemIndex) {
          Lists.checkIndex(itemIndex, items.size());
          return cellPositioner.getSizedCell(itemIndex);
      }
docs: If the item is out of view, instantiates a new cell for the item.
  The returned cell will be properly sized, but not properly positioned
  relative to the cells in the viewport, unless it is itself in the
  viewport.
  
  @return Cell for the given item. The cell will be valid only until the
  next layout pass. It should therefore not be stored. It is intended to
  be used for measurement purposes only.