Use normal equality for const maps.

sdk/lib/_internal/lib/constant_map.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.
 
 part of _js_helper;
 
 abstract class ConstantMap<K, V> implements Map<K, V> {
   const ConstantMap._();
 
   bool get isEmpty => length == 0;
@@ skipping 85 matching lines @@
   // compiler. It is here to make the uninitialized final fields legal.
   GeneralConstantMap(this._jsData) : super._();
 
   // [_jsData] holds a key-value pair list.
   final _jsData;
 
   // We cannot create the backing map on creation since hashCode interceptors
   // have not been defined when constants are created.
   Map<K, V> _getMap() {
     if (JS('bool', r'!this.$map')) {
-      Map backingMap =
-          new LinkedHashMap<K, V>(equals: identical, hashCode: objectHashCode);
+      Map backingMap = new LinkedHashMap<K, V>();
       JS('', r'this.$map = #', fillLiteralMap(_jsData, backingMap));
     }
     return JS('Map', r'this.$map');
   }
 
   bool containsValue(V needle) {
     return _getMap().containsValue(needle);
   }
 
   bool containsKey(Object key) {
@@ skipping 11 matching lines @@
   Iterable<K> get keys {
     return _getMap().keys;
   }
 
   Iterable<V> get values {
     return _getMap().values;
   }
 
   int get length => _getMap().length;
 }