shouldRelayout method

Called whenever a new instance of the custom layout delegate class is provided to the RenderCustomSingleChildLayoutBox object, or any time that a new CustomSingleChildLayout object is created with a new instance of the custom layout delegate class (which amounts to the same thing, because the latter is implemented in terms of the former).

If the new instance represents different information than the old instance, then the method should return true, otherwise it should return false.

If the method returns false, then the getSize, getConstraintsForChild, and getPositionForChild calls might be optimized away.

It's possible that the layout methods will get called even if shouldRelayout returns false (e.g. if an ancestor changed its layout). It's also possible that the layout method will get called without shouldRelayout being called at all (e.g. if the parent changes size).