That's just normal multiple-inheritance. Nothing like mixins.
Mixins would be if the classes actually contribute pieces which combine in an interesting way. Like a border-mixin added to a button class would add to the drawing and to the geometry of the object.
Mixins would be if the classes actually contribute pieces which combine in an interesting way. Like a border-mixin added to a button class would add to the drawing and to the geometry of the object.