Fix all strong-mode warnings.

test/transformer/one_to_many.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library barback.test.transformer.one_to_many;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 import 'mock.dart';
 
 /// A [Transformer] that takes an input asset that contains a comma-separated
 /// list of paths and outputs a file for each path.
 class OneToManyTransformer extends MockTransformer {
   final String extension;
 
   /// Creates a transformer that consumes assets with [extension].
   ///
   /// That file contains a comma-separated list of paths and it will output
   /// files at each of those paths.
   OneToManyTransformer(this.extension);
 
   bool doIsPrimary(AssetId id) => id.extension == ".$extension";
 
-  Future doApply(Transform transform) {
-    return getPrimary(transform)
-        .then((input) => input.readAsString())
-        .then((lines) {
-      for (var line in lines.split(",")) {
-        var id = new AssetId(transform.primaryInput.id.package, line);
-        transform.addOutput(new Asset.fromString(id, "spread $extension"));
-      }
-    });
+  Future doApply(Transform transform) async {
+    var lines = await (await getPrimary(transform)).readAsString();
+    for (var line in lines.split(",")) {
+      var id = new AssetId(transform.primaryInput.id.package, line);
+      transform.addOutput(new Asset.fromString(id, "spread $extension"));
+    }
   }
 
   String toString() => "1->many $extension";
 }