Handle compile-time constants to interfaces.

tests/language/src/CompileTimeConstantFTest.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.
 
 class A {
   final x = 4;
   const A(this.x);
   const A.named([this.x]);
   const A.named2([this.x = 2]);
   const A.named3();
 }
 
 final a1 = const A(0);
 final a2 = const A.named();
 final a3 = const A.named(1);
 final a4 = const A.named2();
 final a5 = const A.named2(3);
 final a6 = const A.named3();
 
 main() {
   Expect.equals(0, a1.x);
   Expect.equals(null, a2.x);
   Expect.equals(1, a3.x);
   Expect.equals(2, a4.x);
   Expect.equals(3, a5.x);
   Expect.equals(4, a6.x);
 }