Add tests for generic methods in strong mode

tests/language_strong/generic_methods_named_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 y});
+typedef FunTypObj = Object Function<T>(T, {Object y});
+typedef FunObjTyp = Object Function<T>(Object, {T y});
+typedef FunTypTyp = Object Function<T>(T, {T y});
+
+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]

Any reason not to also assert here that

funObjObj is FunXY for all X and Y?

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

None at all :) Thanks!

Also added checks for other functions, so that now there's a check for each
function against each of the types.

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

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

Similarly here and below: Might as well have is/is! for all the function types.
In particular, funTypObj is a FunTypTyp but not a FunObjTyp, so the missing
cases are not just "all the same" or otherwise trivial.

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

Agreed and 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);
+}