Enforce use of the forEachInstanceField ordering for constructed constants.

pkg/compiler/lib/src/constants/values.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.
 
 library dart2js.constants.values;
 
 import '../common.dart';
 import '../core_types.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart'
@@ skipping 640 matching lines @@
   }
 
   DartType getType(CoreTypes types) => const DynamicType();
 
   String toDartText() => 'synthetic($kind, $payload)';
 
   String toStructuredText() => 'SyntheticConstant($kind, $payload)';
 }
 
 class ConstructedConstantValue extends ObjectConstantValue {
+  // TODO(johnniwinther): Make [fields] private to avoid misuse of the map
+  // ordering and mutability.
   final Map<FieldElement, ConstantValue> fields;
   final int hashCode;
 
   ConstructedConstantValue(
       InterfaceType type, Map<FieldElement, ConstantValue> fields)
       : this.fields = fields,
         hashCode = Hashing.mapHash(fields, Hashing.objectHash(type)),
         super(type) {
     assert(type != null);
     assert(!fields.containsValue(null));
@@ skipping 102 matching lines @@
 
   @override
   DartType getType(CoreTypes types) => const DynamicType();
 
   @override
   String toStructuredText() => 'NonConstant';
 
   @override
   String toDartText() => '>>non-constant<<';
 }