Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/invoke_call_on_closure_test.dart

 // Copyright (c) 2014, 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_call_on_closure;
 
+@MirrorsUsed(targets: "test.invoke_call_on_closure")
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
 class FakeFunctionCall {
   call(x, y) => '1 $x $y';
 }
 class FakeFunctionNSM {
   noSuchMethod(msg) => msg.positionalArguments.join(', ');
 }
@@ skipping 42 matching lines @@
                 im.invoke(#call, [9, 10]).reflectee);
 
   im = reflect(c.tearOffOpt);
   Expect.equals('33 C 11 12 13 null',
                 im.invoke(#call, [11, 12, 13]).reflectee);
 
   im = reflect(c.tearOffNamed);
   Expect.equals('44 C 14 15 null 16',
                 im.invoke(#call, [14, 15], {#w: 16}).reflectee);
 }