This function is only used by gtk.Container subclasses, to assign a size, position and (optionally) baseline to their child widgets.
In this function, the allocation and baseline may be adjusted. It will be forced to a 1x1 minimum size, and the adjust_size_allocation virtual and adjust_baseline_allocation methods on the child will be used to adjust the allocation and baseline. Standard adjustments include removing the widget's margins, and applying the widget’s halign and valign properties.
If the child widget does not have a valign of GTK_ALIGN_BASELINE the baseline argument is ignored and -1 is used instead.