Issue 3476. Final variables don't have to have constant initializers

runtime/bin/directory_impl.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.
 
 
 class _Directory implements Directory {
   static const CREATE_REQUEST = 0;
   static const DELETE_REQUEST = 1;
   static const EXISTS_REQUEST = 2;
   static const CREATE_TEMP_REQUEST = 3;
@@ skipping 187 matching lines @@
       _directoryService = _newServicePort();
     }
   }
 
   final String _path;
   SendPort _directoryService;
 }
 
 class _DirectoryLister implements DirectoryLister {
   _DirectoryLister(String path, bool recursive) {
-    final int LIST_DIRECTORY = 0;
-    final int LIST_FILE = 1;
-    final int LIST_ERROR = 2;
-    final int LIST_DONE = 3;
+    const int LIST_DIRECTORY = 0;
+    const int LIST_FILE = 1;
+    const int LIST_ERROR = 2;
+    const int LIST_DONE = 3;
 
     final int RESPONSE_TYPE = 0;
     final int RESPONSE_PATH = 1;
     final int RESPONSE_COMPLETE = 1;
     final int RESPONSE_ERROR = 2;
 
     List request = new List(3);
     request[0] = _Directory.LIST_REQUEST;
     request[1] = path;
     request[2] = recursive;
@@ skipping 63 matching lines @@
     } else {
       throw e;
     }
   }
 
   Function _onDir;
   Function _onFile;
   Function _onDone;
   Function _onError;
 }