Handle calls to redirecting factories.

tests/compiler/dart2js/kernel/visitor_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.
 
 /// Test that the dart2js copy of [KernelVisitor] generates the expected IR as
 /// defined by kernel spec-mode test files.
 
 import 'dart:io';
 import 'package:compiler/src/compiler.dart' show Compiler;
 import 'package:compiler/src/js_backend/backend.dart' show JavaScriptBackend;
 import 'package:compiler/src/commandline_options.dart' show Flags;
 import 'package:kernel/text/ast_to_text.dart';
 import 'package:path/path.dart' as pathlib;
 import 'package:test/test.dart';
 
 import '../memory_compiler.dart';
 
 const String TESTCASE_DIR = 'third_party/pkg/kernel/testcases/';
 
 const List<String> SKIP_TESTS = const <String>[
   'DeltaBlue', // Super calls encoded as `super.{...` and not `this.{...`.
-  'external', // 'dart:_isolate_helper' is imported instead of 'dart:isolate'.
 ];
 
 main(List<String> arguments) {
   Directory directory = new Directory('${TESTCASE_DIR}/input');
   for (FileSystemEntity file in directory.listSync()) {
     if (file is File && file.path.endsWith('.dart')) {
       String name = pathlib.basenameWithoutExtension(file.path);
       bool selected = arguments.contains(name);
       if (!selected) {
         if (arguments.isNotEmpty) continue;
@@ skipping 23 matching lines @@
           print('--expected--------------------------------------------------');
           print(expected);
           print('--actual----------------------------------------------------');
           print(actual);
         }
         expect(actual, equals(expected));
       });
     }
   }
 }