Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/method_mirror_properties_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 lib;
+
+@MirrorsUsed(targets: "lib")
 import "dart:mirrors";
 
 import "package:expect/expect.dart";
 
 doNothing42() {}
 
 int _x = 5;
 int get topGetter => _x;
 void set topSetter(x) { _x = x; }
 
@@ skipping 54 matching lines @@
   classMirror = reflectClass(AbstractC);
   checkKinds(classMirror.declarations[#AbstractC],
       [false, false, false, false, true]);
   checkKinds(classMirror.declarations[#bar],
       [false, true, false, false, false]);
   checkKinds(classMirror.declarations[#priv],
       [false, true, true, false, false]);
   checkKinds(classMirror.declarations[const Symbol("priv=")],
       [false, true, false, true, false]);
 }