Fix issue 4639

tests/compiler/dart2js_extra/regress/4639_test.dart

 // Copyright (c) 2012, 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.
 
-class B {
-  const B();
+class A {
+  bool contains(x, y) => true;
 }
 
-class A {
-  var x = const B();
-  A();
+class B {
+  A makeA() => new A();
+  bool test() => makeA().contains(1, 2);
 }
 
 main() {
-  Expect.isTrue(new A().x === new A().x);
+  Expect.isTrue(new B().test());
+  Expect.isTrue("x".contains("x"));
 }