b10728fbac
dart2js previously syntactically matched on `Iterable<T>` and `Stream<T>` exactly and did not compute the union-free type. The new computation is a direct translation of the specified semantics. Change-Id: Iaf916c6ba65e626181663ca554c38c90cdd88899 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/341337 Reviewed-by: Sigmund Cherem <sigmund@google.com> Commit-Queue: Mayank Patke <fishythefish@google.com>