Handle compile-time constants to interfaces.

tests/language/src/CompileTimeConstantHTest.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.
+// Dart test program for testing setting/getting of instance fields.

[ngeoffray, 2012/03/18 13:56:04]

Please update description.

[floitsch, 2012/03/18 18:44:15]

Removed comment.
Done.

+
+class A implements B {
+  final x = 4;
+  const A(this.x);
+}
+
+interface B default A {
+  const B(x);
+}
+
+final b1 = const B(499);
+
+main() {
+  Expect.equals(499, b1.x);
+}