Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/intercepted_class_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.
 
 // Ensure that classes handled specially by dart2js can be reflected on.
 
 library test.intercepted_class_test;
 
+@MirrorsUsed(targets: "dart.core")
 import 'dart:mirrors';
 
 import 'stringify.dart' show stringify, expect;
 
 checkClassMirrorMethods(ClassMirror cls) {
   var variables = new Map();
   cls.declarations.forEach((Symbol key, DeclarationMirror value) {
     if (value is VariableMirror && !value.isStatic && !value.isPrivate) {
       variables[key] = value;
     }
   });
   expect('{}', variables);
 }
 
 checkClassMirror(ClassMirror cls, String name) {
   expect('s($name)', cls.simpleName);
   checkClassMirrorMethods(cls);
 }
 
 main() {
   checkClassMirror(reflectClass(String), 'String');
   checkClassMirror(reflectClass(int), 'int');
   checkClassMirror(reflectClass(double), 'double');
   checkClassMirror(reflectClass(num), 'num');
   checkClassMirror(reflectClass(bool), 'bool');
   checkClassMirror(reflectClass(List), 'List');
 }