CellAllocCallback  
    typealias CellAllocCallback = (renderer: CellRenderer, <Error class: unknown class>, <Error class: unknown class>) -> Boolean(source)
The type of the callback functions used for iterating over the cell renderers and their allocated areas inside a GtkCellArea, see gtk_cell_area_foreach_alloc().
- param - rendererthe cell renderer to operate on
- param - cellAreathe area allocated to @renderer inside the rectangle provided to gtk_cell_area_foreach_alloc().
- param - cellBackgroundthe background area for @renderer inside the background area provided to gtk_cell_area_foreach_alloc().
- return true to stop iterating over cells.