Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/generic_mixin_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.generic_mixin;
 
+@MirrorsUsed(targets: "test.generic_mixin")
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
 import 'generics_helper.dart';
 
 class Super<S> {}
 class Mixin<M> {}
 class Nixim<N> {}
 
@@ skipping 76 matching lines @@
   typeArguments(reflect(new GenericClass2<bool>()).type.mixin, [reflectClass(bool)]);
   typeArguments(reflect(new NonGenericClass1()).type.superclass.mixin, [dynamicMirror]);
   typeArguments(reflect(new NonGenericClass2()).type.superclass.mixin, [reflectClass(String)]);
   typeArguments(reflect(new GenericClass1<bool>()).type.superclass.mixin, [reflectClass(bool)]);
   typeArguments(reflect(new GenericClass2<bool>()).type.superclass.mixin, [reflectClass(String)]);
   typeArguments(reflect(new GenericMultipleMixins<bool, String, int>()).type.mixin, [reflectClass(bool), reflectClass(String), reflectClass(int)]);
   typeArguments(reflect(new GenericMultipleMixins<bool, String, int>()).type.superclass.mixin, [reflectClass(int)]);
   typeArguments(reflect(new GenericMultipleMixins<bool, String, int>()).type.superclass.superclass.mixin, [reflectClass(String)]);
   typeArguments(reflect(new GenericMultipleMixins<bool, String, int>()).type.superclass.superclass.superclass.mixin, [reflectClass(bool)]);
 }