Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/set_field_with_final_inheritance_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.set_field_with_final_inheritance;
 
+@MirrorsUsed(targets: "test.set_field_with_final_inheritance")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 class S {
   var sideEffect = 0;
 
   var mutableWithInheritedMutable = 1;
   final mutableWithInheritedFinal = 2;
   set mutableWithInheritedSetter(x) => sideEffect = 3;
 
@@ skipping 88 matching lines @@
   Expect.equals(26, im.setField(#setterWithInheritedFinal, 26).reflectee);
   Expect.equals(8, c.setterWithInheritedFinal);
   Expect.equals(8, c.superSetterWithInheritedFinal);
   Expect.equals(17, c.sideEffect);
 
   c = new C();
   im = reflect(c);
   Expect.equals(27, im.setField(#setterWithInheritedSetter, 27).reflectee);
   Expect.equals(18, c.sideEffect);
 }