Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/list_tracer3_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.
 
 // We used to always nullify the element type of a list we are tracing in
 // the presence of a fixed length list constructor call.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'package:compiler/src/types/types.dart'
     show ContainerTypeMask, TypeMask;
 
 import 'compiler_helper.dart';
-import 'parser_helper.dart';
 import 'type_mask_test_helper.dart';
 
 
 const String TEST = r'''
 var myList = [];
 var otherList = ['foo', 42];
 main() {
   var a = otherList[0];
   a += 54;
   myList.add(a);
@@ skipping 11 matching lines @@
       ContainerTypeMask mask = typesInferrer.getTypeOfElement(element);
       Expect.equals(type, simplify(mask.elementType, compiler), name);
     }
 
     var interceptorType =
       findTypeMask(compiler, 'Interceptor', 'nonNullSubclass');
 
     checkType('myList', interceptorType);
   }));
 }