Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/simple_inferrer_final_field3_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.
 
 // Test that we are analyzing field parameters correctly.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
-import 'parser_helper.dart';
 import 'type_mask_test_helper.dart';
 
 const String TEST = """
 
 class A {
   final dynamicField;
   A() : dynamicField = 42;
   A.bar(this.dynamicField);
 }
 
@@ skipping 13 matching lines @@
       var cls = findElement(compiler, className);
       var element = cls.lookupLocalMember(fieldName);
       Expect.equals(type,
           simplify(typesInferrer.getTypeOfElement(element), compiler));
     }
 
     checkFieldTypeInClass('A', 'dynamicField',
         findTypeMask(compiler, 'Interceptor', 'nonNullSubclass'));
   }));
 }