Make pub strong-mode clean.

lib/src/asset/dart/serialize/get_input_transform.dart

Index: lib/src/asset/dart/serialize/get_input_transform.dart
diff --git a/lib/src/asset/dart/serialize/get_input_transform.dart b/lib/src/asset/dart/serialize/get_input_transform.dart
index be22f572d918af1a54767751d713cf7ac89eb9e0..328d72d225f8df2784a622c1d9e061da81c07bdd 100644
--- a/lib/src/asset/dart/serialize/get_input_transform.dart
+++ b/lib/src/asset/dart/serialize/get_input_transform.dart
@@ -5,10 +5,9 @@
 import 'dart:async';
 import 'dart:convert';
 
+import 'package:async/async.dart';
 import 'package:barback/barback.dart';
 
-import '../utils.dart';
-
 /// A mixin for transforms that support [getInput] and the associated suite of
 /// methods.
 abstract class GetInputTransform {
@@ -21,7 +20,7 @@ abstract class GetInputTransform {
   }
 
   Stream<List<int>> readInput(AssetId id) =>
-      futureStream(getInput(id).then((input) => input.read()));
+      StreamCompleter.fromFuture(getInput(id).then((input) => input.read()));
 
   Future<bool> hasInput(AssetId id) {
     return getInput(id).then((_) => true).catchError((error) {