Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/initializing_formals_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.initializing_formals;
 
+@MirrorsUsed(targets: "test.initializing_formals")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 class Class<T> {
   int intField;
   bool boolField;
   String stringField;
   T tField;
   dynamic _privateField;
 
@@ skipping 132 matching lines @@
   Expect.equals(#value, pm.simpleName);
   Expect.equals(reflectClass(num), pm.type);
   Expect.isFalse(pm.isNamed);  /// 01: ok
   Expect.isTrue(pm.isFinal);  // N.B.  /// 01: ok
   Expect.isFalse(pm.isOptional);  /// 01: ok
   Expect.isFalse(pm.hasDefaultValue);  /// 01: ok
   Expect.isFalse(pm.isPrivate);
   Expect.isFalse(pm.isStatic);
   Expect.isFalse(pm.isTopLevel);
 }