Insert covariance checks in strong mode.

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

Index: pkg/kernel/testcases/closures/type_variables.dart.expect
diff --git a/pkg/kernel/testcases/closures/type_variables.dart.expect b/pkg/kernel/testcases/closures/type_variables.dart.expect
index bf7dd96b0ee790fcc6942e819c4bb28f3dadeb24..189739dfb54dc7e5bd1b96391b58a3cd67ee8b2c 100644
--- a/pkg/kernel/testcases/closures/type_variables.dart.expect
+++ b/pkg/kernel/testcases/closures/type_variables.dart.expect
@@ -20,7 +20,7 @@ class C<T extends core::Object, S extends core::Object> extends core::Object {
     return new self::Closure#C#baz#function::•<self::C::T, self::C::S>(null);
   }
   static factory •<T extends core::Object, S extends core::Object>() → self::C<self::C::•::T, self::C::•::S> {
-    final dynamic local = new self::Closure#C#function#local::•<self::C::•::T, self::C::•::S>(null);
+    final() → dynamic local = new self::Closure#C#function#local::•<self::C::•::T, self::C::•::S>(null);
     return local.call();
   }
 }