Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/instance_members_with_override_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.instance_members_with_override;
 
+@MirrorsUsed(targets: "test.instance_members_with_override")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 class S {
   var field;
   final finalField = 0;
   method() {}
   get getter {}
   set setter(x) {}
   notOverridden() {}
@@ skipping 57 matching lines @@
   Expect.equals(cMirror, cMirror.instanceMembers[#field].owner);
   Expect.equals(cMirror, cMirror.instanceMembers[const Symbol('field=')].owner);
   Expect.equals(cMirror, cMirror.instanceMembers[#finalField].owner);
   Expect.equals(cMirror, cMirror.instanceMembers[#method].owner);
   Expect.equals(cMirror, cMirror.instanceMembers[#getter].owner);
   Expect.equals(cMirror,cMirror.instanceMembers[const Symbol('setter=')].owner);
 
   Expect.equals(sMirror, sMirror.instanceMembers[#notOverridden].owner);
   Expect.equals(sMirror, cMirror.instanceMembers[#notOverridden].owner);
 }