Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/field_type_simple_inferer_test.dart

Index: tests/compiler/dart2js/field_type_simple_inferer_test.dart
diff --git a/tests/compiler/dart2js/field_type_simple_inferer_test.dart b/tests/compiler/dart2js/field_type_simple_inferer_test.dart
index be6259d569ce404b4eb798df123cca9025d7bce2..2a33d95017d615e7a6ed4e89b61e783f97cb00ad 100644
--- a/tests/compiler/dart2js/field_type_simple_inferer_test.dart
+++ b/tests/compiler/dart2js/field_type_simple_inferer_test.dart
@@ -2,14 +2,12 @@
 // 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:async';
 import 'package:expect/expect.dart';
-import "package:async_helper/async_helper.dart";
+import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
-import 'parser_helper.dart';
 import 'type_mask_test_helper.dart';
 
 void compileAndFind(String code,