tree fa087654ef5de2f8bb224be42d282e3cd29b74e8
parent e6cf09621e8a67cca4ae1998450bb0e224215670
author Mike Fairhurst <mfairhurst@google.com> 1600805929 -0700
committer Mike Fairhurst <mfairhurst@google.com> 1601094247 -0700

Remove unneeded dart:async import

Since Dart 2.1, Future and Stream have been exported from dart:core.

Alternatively, if for some reason this package needs to continue to
support Dart 2.0, an exception can be made for this internally.