function wasMixinPreviouslyApplied(mixin, superClass) {
  let klass = superClass;
  while (klass) {
    if (appliedClassMixins.get(klass) === mixin) {
      return true;
    }
    klass = Object.getPrototypeOf(klass);
  }
  return false;
}
Vefify if the Mixin was previously applyed
@private
@param {function} mixin      Mixin being applyed
@param {object} superClass   Class receiving the new mixin
@returns {boolean}