Currently mixin application is specified as creating forwarding constructors for all generative constructors of the superclass.
The created constructors are not const constructors, making it impossible to create a const class with a mixin.

If the superclass constructor is a const constructor, and the mixin doesn't add any fields, please make the created constructor also a const constructor. That would make it possible to create a const class using a mixin:

  class EmptyList<E> extends Object with ImmutableListMixin<E> {
    int get length => 0;
    int operator[](int i) { throw new RangeError.value(i); }
  }

  ... return const EmptyList(); ...

Not having const constructors makes mixins less useful.