jpaulsen

Implement AVOID using Completer directly.

1

From [Effective Dart](https://www.dartlang.org/guides/language/effective-dart/usage#avoid-using-completer-directly)

Implement PREFER async/await over using raw futures.

2

From [Effective Dart] (https://www.dartlang.org/guides/language/effective-dart/usage#prefer-asyncawait-over-using-raw-futures)

From [Effective Dart](https://www.dartlang.org/guides/language/effective-dart/usage#do-initialize-fields-at-their-declaration-when-possible)