Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/analyze_unused_dart2js_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 analyze_unused_dart2js;
 
 import 'package:async_helper/async_helper.dart';
 
 import '../../../sdk/lib/_internal/compiler/implementation/filenames.dart';
 
 import 'analyze_helper.dart';
 
 const String SIMPLIFY_NEVER_CALLED = "The method 'simplify' is never called";
 
-// The simplify method isn't used in dart2js anymore but is used by many tests.
-const Map<String, List<String>> WHITE_LIST = const {
-  "type_mask.dart": const [SIMPLIFY_NEVER_CALLED],
-  "concrete_types_inferrer.dart": const [SIMPLIFY_NEVER_CALLED],
-};
-
 void main() {
   var uri = currentDirectory.resolve(
       'sdk/lib/_internal/compiler/implementation/use_unused_api.dart');
-  asyncTest(
-      () => analyze([uri], WHITE_LIST, analyzeAll: false));
+  asyncTest(() => analyze([uri], {}, analyzeAll: false));
 }