@mustCallSuper does not error for new mixin syntax

[TastyPi]

• Dart SDK Version (dart --version)
  2.2.1-dev.2.0+google3-v2.2.1.dev.2.0

Consider the following:

class Foo {
  @mustCallSuper
  void bar() {}
}

mixin FooMixin on Foo {
  @override
  void bar() {}
}

I would expect this to fail to build with an error complaining that FooMixin.bar does not call super.bar, instead it builds successfully with no error or warning.