Remove ClassHierarchy factory constructor.

pkg/kernel/test/treeshaker_bench.dart

 // Copyright (c) 2016, 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.
 library kernel.treeshaker_bench;
 
 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
@@ skipping 32 matching lines @@
     exit(1);
   }
   String filename = options.rest.single;
   bool strongMode = options['strong'];
 
   Program program = loadProgramFromBinary(filename);
 
   ClassHierarchy buildClassHierarchy() {
     return options['basic']
         ? new BasicClassHierarchy(program)
-        : new ClassHierarchy(program);
+        : new ClosedWorldClassHierarchy(program);
   }
 
   CoreTypes coreTypes = new CoreTypes(program);
 
   var watch = new Stopwatch()..start();
   ClassHierarchy sharedClassHierarchy = buildClassHierarchy();
   int coldHierarchyTime = watch.elapsedMicroseconds;
   var shaker = new TreeShaker(coreTypes, sharedClassHierarchy, program,
       strongMode: strongMode);
   if (options['diagnose']) {
@@ skipping 24 matching lines @@
 
   var coldShakingMs = coldTreeShakingTime ~/ 1000;
   var coldHierarchyMs = coldHierarchyTime ~/ 1000;
   var hotShakingMs = hotTreeShakingTime ~/ 1000;
   var hotHierarchyMs = hotHierarchyTime ~/ 1000;
 
   print('''
 build.cold $coldShakingMs ms ($coldHierarchyMs ms from hierarchy)
 build.hot  $hotShakingMs ms ($hotHierarchyMs ms from hierarchy)''');
 }