Fix the remaining strong mode warnings.

test/chain/chain_test.dart

Index: test/chain/chain_test.dart
diff --git a/test/chain/chain_test.dart b/test/chain/chain_test.dart
index 40b06d55224fcd8d6811e471d257b09db4bd9963..0824f4f763fd9c3ac63d1683e9b307096e545f9f 100644
--- a/test/chain/chain_test.dart
+++ b/test/chain/chain_test.dart
@@ -10,6 +10,8 @@ import 'package:test/test.dart';
 
 import 'utils.dart';
 
+typedef void ChainErrorCallback(stack, Chain chain);
+
 void main() {
   group('Chain.parse()', () {
     test('parses a real Chain', () {
@@ -48,7 +50,8 @@ void main() {
       }, onError: expectAsync((error, chain) {
         expect(error, equals("oh no"));
         expect(chain, new isInstanceOf<Chain>());
-      }), when: false);
+      }) as ChainErrorCallback, when: false);
+      // TODO(rnystrom): Remove this cast if expectAsync() gets a better type.

[nweiz, 2016/04/08 00:24:03]

I generally haven't been making tests strong mode clean yet, since test itself
isn't strong mode clean and there's not a great way to ensure that they stay
clean.

     });
   });