Add regression test for r24720.

tests/language/regress_r24720_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 that dart2js uses the right interceptor when call a method on
-// something that has type number.
+// Regression test for r24720.
 
 import 'package:expect/expect.dart';
 
-var array = [];
+class A<T> {}
+
+class B extends A<int> {
+  B() : this.foo();
+  B.foo();
+}
 
 main() {
-  array.add(false);
-  var x = array[0] ? 1.5 : 2;
-  Expect.isTrue(x.isEven);
-}
+  Expect.isTrue(new B() is B);
+  Expect.isTrue(new B() is A<int>);
+  Expect.isFalse(new B() is A<String>);
+}