Extract OrderedTypeSetBuilderBase from OrderedTypeSetBuilder

tests/compiler/dart2js/class_set_test.dart

 // Copyright (c) 2015, 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 for iterators on for [SubclassNode].
 
 library class_set_test;
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'type_test_helper.dart';
-import 'package:compiler/src/elements/elements.dart' show Element, ClassElement;
+import 'package:compiler/src/elements/elements.dart' show ClassElement;
 import 'package:compiler/src/universe/class_set.dart';
 import 'package:compiler/src/util/enumset.dart';
 import 'package:compiler/src/util/util.dart';
 import 'package:compiler/src/world.dart';
 
 void main() {
   asyncTest(() async {
     await testIterators();
     await testForEach();
   });
@@ skipping 553 matching lines @@
   checkAny(B, [B, D], find: D, anySubtype: true, expectedResult: true);
   checkAny(B, [B, D, F, I], find: I, anySubtype: true, expectedResult: true);
 
   checkAny(X, [X, A, B, D, C, G, F, I, H, E],
       anySubtype: true, expectedResult: false);
   checkAny(X, [X, A], find: A, anySubtype: true, expectedResult: true);
   checkAny(X, [X, A, B, D], find: D, anySubtype: true, expectedResult: true);
   checkAny(X, [X, A, B, D, C, G, F, I],
       find: I, anySubtype: true, expectedResult: true);
 }