Support jsinterop/world_test from .dill

tests/compiler/dart2js/jsinterop/world_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 jsinterop.world_test;
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common_elements.dart';
 import 'package:compiler/src/elements/entities.dart' show ClassEntity;
 import 'package:compiler/src/elements/names.dart';
 import 'package:compiler/src/universe/selector.dart';
 import 'package:compiler/src/world.dart';
 import '../type_test_helper.dart';
 
 void main() {
   asyncTest(() async {
-    await testClasses();
+    await testClasses(CompileMode.memory);
+    await testClasses(CompileMode.dill);
   });
 }
 
-testClasses() async {
+testClasses(CompileMode compileMode) async {
   test(String mainSource,
       {List<String> directlyInstantiated: const <String>[],
       List<String> abstractlyInstantiated: const <String>[],
       List<String> indirectlyInstantiated: const <String>[]}) async {
     TypeEnvironment env = await TypeEnvironment.create(r"""
 @JS()
 class A {
   get foo;
 
   external A(var foo);
@@ skipping 37 matching lines @@
 newA() => new A(0);
 newB() => new B(1);
 newC() => new C(foo: 2);
 newD() => new D(foo: 3);
 newE() => new E(4);
 newF() => new F(5);
 """, mainSource: """
 import 'package:js/js.dart';
 
 $mainSource
-""", compileMode: CompileMode.memory);
+""", compileMode: compileMode);
     Map<String, ClassEntity> classEnvironment = <String, ClassEntity>{};
 
     ClassEntity registerClass(ClassEntity cls) {
       classEnvironment[cls.name] = cls;
       return cls;
     }
 
     ClosedWorld world = env.closedWorld;
     ElementEnvironment elementEnvironment = world.elementEnvironment;
     ClassEntity Object_ = registerClass(world.commonElements.objectClass);
@@ skipping 104 matching lines @@
 
   await test('main() => newE();', directlyInstantiated: ['E']);
 
   await test('main() => newF();', directlyInstantiated: ['F']);
 
   await test('main() => [newD(), newE()];',
       directlyInstantiated: ['E'],
       abstractlyInstantiated: ['A', 'B', 'C', 'D'],
       indirectlyInstantiated: ['Object', 'Interceptor', 'JavaScriptObject']);
 }