Implement is-checks against type variables.

tests/language/generic2_test.dart

+// Copyright (c) 2013, 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.
+
+// Test is-tests with type variables.
+
+class A<T> {
+  foo(o) => o is T;
+}
+
+class B {}
+
+class C extends A<int> {}
+
+main() {
+  Expect.isTrue(new A<Object>().foo(new B()));
+  Expect.isTrue(new A<Object>().foo(1));
+  Expect.isFalse(new A<int>().foo(new Object()));
+  Expect.isFalse(new A<int>().foo('hest'));
+  Expect.isTrue(new A<B>().foo(new B()));
+  Expect.isFalse(new A<B>().foo(new Object()));
+  Expect.isFalse(new A<B>().foo(1));
+  Expect.isTrue(new C().foo(1));
+  Expect.isFalse(new C().foo(new Object()));
+  Expect.isFalse(new C().foo('hest'));
+  Expect.isTrue(new A<List<int>>().foo(new List<int>()));
+  Expect.isFalse(new A<List<int>>().foo(new List<String>()));
+}