dart2dart: fix top level field declarations.

tests/compiler/dart2js/unparser_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.
 
 #import('dart:uri');
 #import('parser_helper.dart');
 #import("../../../lib/compiler/compiler.dart");
 #import("../../../lib/compiler/implementation/tree/tree.dart");
 
 testUnparse(String statement) {
@@ skipping 93 matching lines @@
 
 main() {
   should_be_kept();
 }
 ''';
   testDart2Dart(src, (String s) {
     Expect.equals('should_be_kept(){}main(){should_be_kept();}', s);
   });
 }
 
+testTopLevelField() {
+  final src = 'final String x="asd";main(){x;}';
+  testDart2Dart(src, (String s) => Expect.equals(src, s));
+}
+
 main() {
   testGenericTypes();
   testForLoop();
   testEmptyList();
   testClosure();
   testIndexedOperatorDecl();
   testNativeMethods();
   testPrefixIncrements();
   testSimpleFileUnparse();
+  testTopLevelField();
 }