Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/list_constructor_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.
 
+library lib;
+
 import "package:expect/expect.dart";
 
+@MirrorsUsed(targets: const ["lib", "dart.core"])
 import 'dart:mirrors';
 
 main() {
   var cls = reflectClass(List);
   Expect.throws(() => cls.newInstance(const Symbol(''), [null]),
                 (e) => e is ArgumentError);
 
   var list = cls.newInstance(const Symbol(''), [42]).reflectee;
   // Check that the list is fixed.
   Expect.equals(42, list.length);
   Expect.throws(() => list.add(2), (e) => e is UnsupportedError);
   list[0] = 1;
   Expect.equals(1, list[0]);
 
   testGrowableList(); /// 01: ok
 }
 
 testGrowableList() {
   var cls = reflectClass(List);
   var list = cls.newInstance(const Symbol(''), []).reflectee;
   // Check that the list is growable.
   Expect.equals(0, list.length);
   list.add(42);
   Expect.equals(1, list.length);
 }