Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/parameter_metadata_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 test.parameter_metadata_test;
 
+@MirrorsUsed(targets: "test.parameter_metadata_test")
 import 'dart:mirrors';
 
 import 'metadata_test.dart';
 
 const m1 = 'm1';
 const m2 = #m2;
 const m3 = const CustomAnnotation(3);
 
 class CustomAnnotation {
   final value;
@@ skipping 37 matching lines @@
   checkMetadata(mm.parameters[0], []);
   checkMetadata(mm.parameters[1], []);
 
   mm = cm.declarations[#corge];
   checkMetadata(mm.parameters[0], [m1]);
   checkMetadata(mm.parameters[1], [m2]);
 
   mm = cm.declarations[const Symbol('x=')];
   checkMetadata(mm.parameters[0], [m2]);
 }