assert clazz.isClass(): Debug.show(clazz);
assert clazz.isClassType(): Debug.show(clazz);
    public This This(int pos, Symbol clazz) {        assert clazz.isClass(): Debug.show(clazz);        This tree = make.This(pos, clazz);        global.nextPhase();        tree.setType(clazz.thisType());        global.prevPhase();        return tree;    }