Fix some tests that were broken in the library tag removal.

test/dart2js/compiles_imported_generated_file_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import '../serve/utils.dart';
 
@@ skipping 10 matching lines @@
       }),
       d.dir("lib", [
         d.file("transformer.dart", dartTransformer("munge"))
       ]),
       d.dir("web", [
         d.file("main.dart", """
 import "other.dart";
 void main() => print(TOKEN);
 """),
         d.file("other.dart", """
+const TOKEN = "before";
 """)
       ])
     ]).create();
 
     pubGet();
     pubServe();
     requestShouldSucceed("main.dart.js", contains("(before, munge)"));
     endPubServe();
   });
 }