Handle compile-time constants to interfaces.

tests/language/src/CompileTimeConstantHTest.dart

Index: tests/language/src/CompileTimeConstantHTest.dart
diff --git a/tests/language/src/CompileTimeConstantHTest.dart b/tests/language/src/CompileTimeConstantHTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..734f6f8a9754a08d43309aa711b6ca54a8f8347b
--- /dev/null
+++ b/tests/language/src/CompileTimeConstantHTest.dart
@@ -0,0 +1,18 @@
+// 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 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);
+}