Add mirrors to whitelist again. It was removed in a previous cl, because it was

tests/compiler/dart2js/analyze_test_test.dart

 // Copyright (c) 2016, 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 dart2js.analyze_test.test;
 
 import 'dart:io';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/apiimpl.dart' show
@@ skipping 11 matching lines @@
  * Map of white-listed warnings and errors.
  *
  * Use an identifiable suffix of the file uri as key. Use a fixed substring of
  * the error/warning message in the list of white-listings for each file.
  */
 // TODO(johnniwinther): Support canonical URIs as keys and message kinds as
 // values.
 const Map<String, List/*<String|MessageKind>*/> WHITE_LIST = const {
   // Several tests import mirrors; any of these might trigger the warning.
   ".dart": const [
+      MessageKind.IMPORT_EXPERIMENTAL_MIRRORS,
   ],
   "/test/src/util/": const [
       "Library 'package:async/async.dart' doesn't export a "
       "'ForkableStream' declaration.",
   ],
   "mirrors_test.dart": const [
       MessageKind.INVALID_SYMBOL,
       MessageKind.PRIVATE_IDENTIFIER,
   ],
 };
@@ skipping 31 matching lines @@
       if (entity is File && entity.path.endsWith('.dart')) {
         Uri file = Uri.base.resolve(nativeToUriPath(entity.path));
         if (!SKIP_LIST.any((skip) => file.path.contains(skip))) {
           uriList.add(file);
         }
       }
     }
     await analyze(uriList, WHITE_LIST, mode: AnalysisMode.URI);
   });
 }