Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/invoke_closurization_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.invoke_closurization_test;
 
+@MirrorsUsed(targets: "test.invoke_closurization_test")
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
 class C {
   instanceMethod(x, y, z) => '$x+$y+$z';
   static staticFunction(x, y, z) => '$x-$y-$z';
 }
 libraryFunction(x, y, z) => '$x:$y:$z';
 
@@ skipping 13 matching lines @@
 
   LibraryMirror lm = cm.owner;
   result = lm.getField(#libraryFunction);
   Expect.isTrue(result.reflectee is Function, "Should be closure");
   Expect.equals("A:B:C", result.reflectee('A', 'B', 'C'));
 }
 
 main() {
   testSync();
 }