With the new class hierarchy builder and mixin stubs we no longer
insert superfluous forwarding stub nor use mixin declaration/clones
as targets inconsistently.
These test expand upon existing tests to verify that these issue have
been fixed.
Change-Id: I27db6e27e86d8c83692e9a16f7c435f633a599c3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/194787
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Johnni Winther
8baa649665