Fix warnings in tests.

tests/lib/mirrors/unused_mirrors_test.dart

 // Copyright (c) 2014, 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.
 
 // Tests that MirrorsUsed without usage of the static field does not crash
 // dart2js.
 
 @MirrorsUsed(targets: const ["foo"])
 import 'dart:mirrors';
 
 Bar foo = new Bar();
 
 typedef int FunctionTypeDef();
 
 class Bar {
   final FunctionTypeDef gee;
+  Bar() : gee = (() => 499);
 }
 
 main() {
   // Don't do anything.
 }