Remove deprecated string features.

pkg/serialization/test/polyfill_identity_map_test.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.
 
 /**
  * Provide a trivial test for identity based hashed collections, which we
  * provide here until an implementation is available in the regular libraries.
  */
 // TODO(alanknight): Remove once identity-hashed collections are available.
 // Issue 4161.
@@ skipping 22 matching lines @@
     expect(map.length, 1);
     expect(identityMap.length, 2);
     for (var each in identityMap.values) {
       expect(each, one);
     }
   });
 
   test('uniquing primitives', () {
     var map = new IdentityMap();
     var one = 'one';
-    var two = new String.fromCharCodes(one.charCodes);
+    var two = new String.fromCharCodes(one.codeUnits);
     map[one] = 1;
     expect(map[two], 1);
     expect(map[one], 1);
   });
-}
+}