Add regression test for r24720.

tests/language/regress_r24720_test.dart

Index: tests/language/regress_r24720_test.dart
diff --git a/tests/language/interceptor7_test.dart b/tests/language/regress_r24720_test.dart
similarity index 56%
copy from tests/language/interceptor7_test.dart
copy to tests/language/regress_r24720_test.dart
index 965ddfc800c1b1fa7971bd918391b1e806c00cf3..57380f6324ed5609e3009515d39683fe8a0c6774 100644
--- a/tests/language/interceptor7_test.dart
+++ b/tests/language/regress_r24720_test.dart
@@ -2,15 +2,19 @@
 // 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> {}
 
-main() {
-  array.add(false);
-  var x = array[0] ? 1.5 : 2;
-  Expect.isTrue(x.isEven);
+class B extends A<int> {
+  B() : this.foo();
+  B.foo();
 }
+
+main() {
+  Expect.isTrue(new B() is B);
+  Expect.isTrue(new B() is A<int>);
+  Expect.isFalse(new B() is A<String>);
+}