Add more tests for boxed variables.

tests/compiler/dart2js/closure/closure_test.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:io' hide Link;
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/closure.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/diagnostics/diagnostic_listener.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/entities.dart';
 import 'package:compiler/src/kernel/element_map.dart';
 import 'package:compiler/src/kernel/kernel_backend_strategy.dart';
 import 'package:compiler/src/js_model/locals.dart';
 import 'package:compiler/src/tree/nodes.dart' as ast;
 import 'package:compiler/src/util/util.dart';
 import 'package:expect/expect.dart';
 import '../equivalence/id_equivalence.dart';
 import '../equivalence/id_equivalence_helper.dart';
 import 'package:kernel/ast.dart' as ir;
 
+// TODO(johnnniwinther,efortuna): Enable the these tests for .dill.
+const List<String> whiteList = const <String>[
+  'nested_closures.dart',
+  'mixed.dart',
+];
+
 main(List<String> args) {
   bool verbose = args.contains('-v');
   asyncTest(() async {
     Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
     await for (FileSystemEntity entity in dataDir.list()) {
       print('----------------------------------------------------------------');
       print('Checking ${entity.uri}');
       print('----------------------------------------------------------------');
       String annotatedCode = await new File.fromUri(entity.uri).readAsString();
       print('--from source---------------------------------------------------');
       await checkCode(annotatedCode, computeClosureData, compileFromSource,
           verbose: verbose);
-      // TODO(johnnniwinther,efortuna): Enable the these tests for .dill.
-      if (['nested_closures.dart'].contains(entity.uri.pathSegments.last)) {
+      if (whiteList.contains(entity.uri.pathSegments.last)) {
         print('--skipped for dill--------------------------------------------');
         continue;
       }
       print('--from dill-----------------------------------------------------');
       await checkCode(annotatedCode, computeKernelClosureData, compileFromDill,
           verbose: verbose);
     }
   });
 }
 
@@ skipping 276 matching lines @@
         if (value != '') {
           sb.write('=');
           sb.write(value);
         }
         needsComma = true;
       }
     }
     return sb.toString();
   }
 }