Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/mirror_in_static_init_test.dart

 // Copyright (c) 2015, 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.
 
 // Error in class finalization triggered via mirror in a static initializer.
 // Simply check that we do not crash.
 // This is a regression test for the VM.
 
 library mirror_in_static_init_test;
 
+@MirrorsUsed(targets: "mirror_in_static_init_test")
 import 'dart:mirrors';
 
 // This class is only loaded during initialization of `staticField`.
 abstract class C {
   int _a;
 // This is a syntax error on purpose.
   C([this._a: 0]); /// 01: compile-time error
 }
 
 final int staticField = () {
   var lib = currentMirrorSystem().findLibrary(#mirror_in_static_init_test);
   var lst = new List.from(lib.declarations[#C].declarations.values);
   return 42;
 }();
 
 main() {
   return staticField;
 }