Make native implementation classes for classes that are used as targets in @MirrorsUsed available f…

tests/compiler/dart2js_extra/mirrors_used_native_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')
+import 'dart:mirrors';
+
 import 'package:expect/expect.dart';
 
 main() {
-  Expect.throws(() => double.INFINITY.floor(), (e) => e is UnsupportedError);
-  Expect.throws(() => double.NEGATIVE_INFINITY.floor(),
+  List;  // work-around for a bug in the type-variable handler. TODO(zarah): remove.
+  Expect.equals(3, reflect([1, 2, 3]).getField(#length).reflectee);
+  Expect.throws(() => reflect({"hest": 42}).getField(#length),
                 (e) => e is UnsupportedError);
-  Expect.throws(() => double.NAN.floor(), (e) => e is UnsupportedError);
 }