Use growable lists.

dart/tests/lib/mirrors/mirrors_used_merge_test.dart

 // Copyright (c) 2013, 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.
 
-@MirrorsUsed(targets: 'List')
+/// Test that two MirrorsUsed annotations can be merged with out crashing
+/// dart2js.
+
+@MirrorsUsed(symbols: const ['foo'])
+@MirrorsUsed(symbols: const ['bar'])
 import 'dart:mirrors';
 
-import 'package:expect/expect.dart';
-
 main() {
-  Expect.equals(3, reflect([1, 2, 3]).getField(#length).reflectee);
-  Expect.throws(() => reflect({"hest": 42}).getField(#length),
-                (e) => e is UnsupportedError);
+  // Do nothing, just make sure that merging the annotations doesn't crash
+  // dart2js.
 }