Trait freya::prelude::LayoutMeasurer  
pub trait LayoutMeasurer<Key>where
    Key: NodeKey,{
    // Required methods
    fn measure(
        &mut self,
        node_id: Key,
        node: &Node,
        size: &Size2D<f32, Measure>,
    ) -> Option<(Size2D<f32, Measure>, Arc<SendAnyMap>)>;
    fn should_measure_inner_children(&mut self, node_id: Key) -> bool;
    // Provided method
    fn notify_layout_references(
        &self,
        _node_id: Key,
        _area: Rect<f32, Measure>,
        _inner_sizes: Size2D<f32, Measure>,
    ) { ... }
}