We should implement equivalent functionality to RenderBox::absoluteContentBox for columns and column group elements (i.e. RenderTableCol). By implementing this or a similar method we can resolve other bugs that depend on knowing the dimensions of a column or column group, including bug #15277. Note, we seem to be calculating some or all of the dimensions of columns/column groups in various parts of AutoTableLayout and FixedTableLayout, but do not expose this data.