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* 99% of these are `Future ` --> `Future<void> ` * There are some `test_` methods which declare a return type of `Future` which is non-idiomatic, I think, but in order to create a pragmatic consistency, I added `<void>` to the few test methods in these libraries. Later if we desire, we can remove all of the return types. * Also a few `Completer ` --> `Completer<void> ` and `Stream ` --> `Stream<Object?> ` * There are many remaining cases in `lib/` Change-Id: I41cd51bab6886788e15ac7065dd21e95e789d09f Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/287260 Reviewed-by: Brian Wilkerson <brianwilkerson@google.com> Reviewed-by: Konstantin Shcheglov <scheglov@google.com> Commit-Queue: Samuel Rawlins <srawlins@google.com>