Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/use_strict_test.dart

 // Copyright (c) 2011, 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:async';
-
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'memory_compiler.dart';
 
 // Use strict does not allow parameters or locals named "arguments" or "eval".
 
 const MEMORY_SOURCE_FILES = const {
     'main.dart': '''
       class A {
         final arguments;
@@ skipping 43 matching lines @@
         .where((String line) => !commentLine.hasMatch(line))
         .join("\n");
 
     // TODO(floitsch): we will need to adjust this filter if we start using
     // 'eval' or 'arguments' ourselves. Currently we disallow any 'eval' or
     // 'arguments'.
     RegExp re = new RegExp(r'[^\w$](arguments|eval)[^\w$]');
     Expect.isFalse(re.hasMatch(filtered));
   });
 }