Analyzer does not allow mixins to be derived from classes with super-invocations.

[lrhn]

The Dart 2 specification rolled back the ability to derive a mixin from a class with a superclass other than Object It did not reintroduce the rule that made it an error to derive a mixin from a class with a super-invocation.

The analyzer rejects mixins derived from classes with super-invocations.
Since those super-invocations are necessarily on members of Object, there is no need to disallow them.

The front-end does allow super-invocations in mixins derived from objects, for example:

class C {
  toString() => "[${super.toString()}]";
}
class D {
  toString() => "Yep!";
}
class E = D with C;
main() {
  print(E());  // "[Yep!]"
}

This runs in the VM and dart2js, and should be accepted by the analyzer too.