Add some tests for calls with checks in strong mode.

tests/language_strong/covariant_subtyping_unsafe_call2_test.dart

Index: tests/language_strong/covariant_subtyping_unsafe_call2_test.dart
diff --git a/tests/language_strong/covariant_subtyping_unsafe_call2_test.dart b/tests/language_strong/covariant_subtyping_unsafe_call2_test.dart
index ea5920384df7cd4e5a73ecfb0d1595d2e5090864..5e45c375aa5b9f1fcd0dead2c306d81186b8d7a8 100644
--- a/tests/language_strong/covariant_subtyping_unsafe_call2_test.dart
+++ b/tests/language_strong/covariant_subtyping_unsafe_call2_test.dart
@@ -4,11 +4,11 @@
 import 'package:expect/expect.dart';
 
 class Implementation {
-  method(int x) {}
+  dynamic method(int x) {}
 }
 
 abstract class Interface<T> {
-  method(T x);
+  dynamic method(T x);
 }
 
 class Subclass extends Implementation implements Interface<int> {}