Begin writing tests of the runtime checks needed for Dart 2.0 soundness.

pkg/front_end/testcases/runtime_checks/contravariant_generic_method_type_parameter.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/*@testedFeatures=checks*/
+library test;
+
+typedef void F<T>(T t);
+
+class C<T> {
+  void f<U extends F<T>>(U x) {}
+}
+
+void g(C<num> c) {
+  c.f<F<Object>>((Object o) {});
+}
+
+void test() {
+  g(new C<int>());
+}
+
+void main() {}