Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/map_tracer_keys_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.
 
 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';
 
 
 String generateTest(String key, String value, bool initial) {
   return """
 double aDouble = 42.5;
 List aList = [42];
 
 consume(x) => x;
 
 main() {
@@ skipping 45 matching lines @@
     Expect.isTrue(aListType is ContainerTypeMask);
     ContainerTypeMask container = aListType;
     TypeMask elementType = container.elementType;
     if (bail) {
       Expect.equals(elementType, typesTask.dynamicType);
     } else {
       Expect.equals(elementType, typesTask.uint31Type);
     }
   }));
 }