This clears all of the implicit `Future<dynamic>` types in lib/.
Also a few `extends XyzVisitor<(implicit) dynamic>` are made into
`extends XyzVisitor<void>`.
Also a few raw Stream, StreamController, and Completer types.
Change-Id: I2471cc56d2d2d0545e5e103fff3189e745a54b49
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/287245
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Sam Rawlins
8a9188aae5