Insert covariance checks in strong mode.

pkg/kernel/testcases/closures/named_closure.dart.expect

Index: pkg/kernel/testcases/closures/named_closure.dart.expect
diff --git a/pkg/kernel/testcases/closures/named_closure.dart.expect b/pkg/kernel/testcases/closures/named_closure.dart.expect
index ae1d5a643c2650ea89d9bf9b7541de92cb8d0048..c1b236d5e9dc389776cf25f116df51af948d571c 100644
--- a/pkg/kernel/testcases/closures/named_closure.dart.expect
+++ b/pkg/kernel/testcases/closures/named_closure.dart.expect
@@ -23,7 +23,7 @@ static method main(dynamic arguments) → dynamic {
   final mock::Context #context = new mock::Context::•(1);
   #context.parent = null;
   #context.[]=(0, arguments);
-  final dynamic g = new self::Closure#main#g::•(#context);
+  final(dynamic) → dynamic g = new self::Closure#main#g::•(#context);
   self::f = g;
   self::foo();
 }