Remove deprecated string features.

pkg/serialization/test/polyfill_identity_map_test.dart

Index: pkg/serialization/test/polyfill_identity_map_test.dart
diff --git a/pkg/serialization/test/polyfill_identity_map_test.dart b/pkg/serialization/test/polyfill_identity_map_test.dart
index 9988dcaf574f5bb0d07db9773262a2676aeec749..bfc8fef647686ac2ac1ccdf6941bb410f6ee7eb5 100644
--- a/pkg/serialization/test/polyfill_identity_map_test.dart
+++ b/pkg/serialization/test/polyfill_identity_map_test.dart
@@ -40,9 +40,9 @@ main() {
   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);
   });
-}
+}