Add 'part of' in dart2js code.

lib/compiler/implementation/types/concrete_types_inferrer.dart

Index: lib/compiler/implementation/types/concrete_types_inferrer.dart
diff --git a/lib/compiler/implementation/types/concrete_types_inferrer.dart b/lib/compiler/implementation/types/concrete_types_inferrer.dart
index 93121ba510b3a003e5abcb61eb349757d801844e..8e5ee6cf999b11a7477cf08477296817fd22be16 100644
--- a/lib/compiler/implementation/types/concrete_types_inferrer.dart
+++ b/lib/compiler/implementation/types/concrete_types_inferrer.dart
@@ -2,6 +2,8 @@
 // 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 types;
+
 class CancelTypeInferenceException {
   final Node node;
   final String reason;