Handle constants that mix eager and deferred types.

dart/tests/compiler/dart2js_extra/deferred/deferred_class_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_class_test.dart.
 
 library deferred_class_library;
 
 class MyClass {
   const MyClass();
 
   foo(x) {
     print('MyClass.foo($x)');
     return (x - 3) ~/ 2;
   }
 }
+
+class Constant {
+  final value;
+  const Constant(this.value);
+
+  operator==(other) => other is Constant && value == other.value;
+}