fix unsound cast failures in tests

tests/language_strong/async_test.dart

Index: tests/language_strong/async_test.dart
diff --git a/tests/language_strong/async_test.dart b/tests/language_strong/async_test.dart
index 48b4fda283986ef9e27d88e0377b6bd0e9fd27ef..7d8b2dc1f0ab9fcf4d8a08c3f30b1a39d3379ccc 100644
--- a/tests/language_strong/async_test.dart
+++ b/tests/language_strong/async_test.dart
@@ -45,7 +45,7 @@ class B {
 }
 
 main() {
-  var asyncReturn;
+  Future asyncReturn;
 
   asyncReturn = topLevelFunction();
   Expect.isTrue(asyncReturn is Future);
@@ -94,7 +94,7 @@ main() {
   };
   asyncReturn = moreNesting(1, "ignore", 2);
   Expect.isTrue(asyncReturn is Future);
-  asyncReturn.then((int result) => Expect.equals(result, 28));
+  asyncReturn.then((num result) => Expect.equals(result, 28));
 
   var checkAsync = (var someFunc) {
     var toTest = someFunc();