Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/generic_class_declaration_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';
 
 import 'stringify.dart';
 
 class A<T> {
   var instanceVariable;
   get instanceGetter => null;
   set instanceSetter(x) => x;
   instanceMethod() => null;
@@ skipping 59 matching lines @@
   'constructors');
 
   Expect.setEquals(
       ['TypeVariable(s(T) in s(A), upperBound = Class(s(Object) in '
        's(dart.core), top-level))'],
        cm.declarations.values
          .where((dm) => dm is TypeVariableMirror).map(stringify),
   'type variables');
 
 }