Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/side_effect_tdiv_regression_test.dart

 // Copyright (c) 2013, 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 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 
 import 'compiler_helper.dart';
-import 'parser_helper.dart';
 
 const String TEST = r'''
 class A {
   var field = 42;
 }
 main() {
   var a = new A();
   var b = [42, -1];
   // Force a setter on [field].
   if (false) a.field = 12;
   var c = a.field;
   print(b[0] ~/ b[1]);
   return c + a.field;
 }
 ''';
 
 void main() {
   asyncTest(() => compileAll(TEST).then((generated) {
     Expect.isTrue(generated.contains('return c + c;'));
-  }));  
+  }));
 }