* Pure interfaces marked `interface`. That's most public classes.
* `Stream` made `mixin class`, as a proper skeleton/base implementation.
* `Zone` classes made all `final`.
Added some `<void>` to raw `Future` types.
CoreLibraryReviewExempt: Aske is away.
Tested: No functionality change, only added restrictions.
Change-Id: I91d09fbcdba7d0dfdff3887bc7c9d54364c88b05
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/289221
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>
Commit-Queue: Lasse Nielsen <lrn@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
Lasse R.H. Nielsen
162ff41b0e