Support use of dill in TypeEnv tests

tests/compiler/dart2js/instantiated_classes_test.dart

 // Copyright (c) 2014, 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 instantiated_classes_test;
 
 import 'dart:async';
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/elements/entities.dart'
@@ skipping 44 matching lines @@
 
 Future test(String source, List<String> directlyInstantiatedClasses,
     [List<String> newClasses = const <String>["Class"]]) {
   StringBuffer mainSource = new StringBuffer();
   mainSource.write('main() {\n');
   for (String newClass in newClasses) {
     mainSource.write('  new $newClass();\n');
   }
   mainSource.write('}');
   return TypeEnvironment
-      .create(source, mainSource: mainSource.toString(), useMockCompiler: true)
+      .create(source,
+          mainSource: mainSource.toString(), compileMode: CompileMode.mock)
       .then((dynamic env) {
     LibraryEntity mainLibrary =
         env.compiler.frontendStrategy.elementEnvironment.mainLibrary;
     Iterable<ClassEntity> expectedClasses =
         directlyInstantiatedClasses.map(env.getElement);
     Iterable<ClassEntity> actualClasses = env
         .compiler.resolutionWorldBuilder.directlyInstantiatedClasses
         .where((c) => c.library == mainLibrary);
     Expect.setEquals(expectedClasses, actualClasses);
   });
 }