Handle constants that mix eager and deferred types.

dart/tests/lib/async/deferred/deferred_constant_library.dart

 // Copyright (c) 2013, 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.
 
-// Imported by deferred_function_test.dart and
-// deferred_semantics_test.dart.
+library deferred_constant_library;
 
-library deferred_function_library;
+class Constant {
+  final value;
+  const Constant(this.value);
 
-foo(x) {
-  print('foo($x)');
-  return 42;
+  operator==(other) => other is Constant && value == other.value;
 }