If the child has not marked its own layout as dirty, the child can
return immediately from layout, cutting off the walk, as long as the
parent gives the child the same constraints as the child received
during the previous layout.

Whenever a parent calls a child’s layout method, the parent indicates
whether it uses the size information returned from the child. If,
as often happens, the parent does not use the size information,
then the parent need not recompute its layout if the child selects
a new size because the parent is guaranteed that the new size will
conform to the existing constraints.