Add tests for generic methods in strong mode

tests/language_strong/generic_methods_optional_parameters_test.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.
+
+library generic_methods_optional_parameters_test;
+
+import "package:expect/expect.dart";
+
+typedef FunObjObj = Object Function<T>(Object, [Object]);
+typedef FunTypObj = Object Function<T>(T, [Object]);
+typedef FunObjTyp = Object Function<T>(Object, [T]);
+typedef FunTypTyp = Object Function<T>(T, [T]);
+
+Object funObjObj<T>(Object x, [Object y]) => x;
+Object funTypObj<T>(T x, [Object y]) => y;
+Object funObjTyp<T>(Object x, [T y]) => x;
+Object funTypTyp<T>(T x, [T y]) => null;
+
+main() {
+  Expect.isTrue(funObjObj is FunObjObj);

[Leaf, 2017/03/09 05:51:19]

As in the previous test, maybe check funObjObj against all of the types?

[Dmitry Stefantsov, 2017/03/10 13:21:54]

Done.

+
+  Expect.isTrue(funTypObj is FunTypObj);
+  Expect.isTrue(funTypObj is! FunObjObj);

[eernst, 2017/03/09 14:55:02]

Same comment as in the previous test from me, too. ;-)

[Dmitry Stefantsov, 2017/03/10 13:21:54]

Agree here as well :) Done.

+
+  Expect.isTrue(funObjTyp is FunObjTyp);
+  Expect.isTrue(funObjTyp is! FunObjObj);
+
+  Expect.isTrue(funTypTyp is FunTypTyp);
+  Expect.isTrue(funTypTyp is! FunTypObj);
+  Expect.isTrue(funTypTyp is! FunObjTyp);
+  Expect.isTrue(funTypTyp is! FunObjObj);
+}