0b03e711bf
Make better error message for mixins since they can't be final nor sealed. Bug: https://github.com/dart-lang/sdk/issues/52697 Change-Id: I56a9cb66131c0a47ea1c91b95dcf70d12835134e Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/308964 Commit-Queue: Kallen Tu <kallentu@google.com> Reviewed-by: Johnni Winther <johnniwinther@google.com>