fixLayout is now renamed to layoutSubmorphs, just like in Cuis
Layout classes enhancements - first working example (see details)

open an inspector and paste, then doIt:

var inspector, world, row;
rect1 = new RectangleMorph();
rect2 = new RectangleMorph();
world = (this.world instanceof Function ? this.world() : this.root() ||
this.world);

row = LayoutMorph.newRow()
row.addMorphProportionalWidth(rect1,2)
row.addMorphProportionalWidth(rect2,1)
row.layoutSubmorphs()
row.setPosition(world.hand.position());
row.keepWithin(world);
world.add(row);
row.changed();