Remove ClassHierarchy factory constructor.

pkg/kernel/test/type_subtype_test.dart

Index: pkg/kernel/test/type_subtype_test.dart
diff --git a/pkg/kernel/test/type_subtype_test.dart b/pkg/kernel/test/type_subtype_test.dart
index 7e1b5fdd85f529a1c91afabf548b5e98f47ed256..b6d7b373075d673573677a20f43689d033814783 100644
--- a/pkg/kernel/test/type_subtype_test.dart
+++ b/pkg/kernel/test/type_subtype_test.dart
@@ -2,6 +2,7 @@
 // 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:kernel/src/incremental_class_hierarchy.dart';
 import 'package:test/test.dart';
 import 'package:kernel/ast.dart';
 import 'package:kernel/class_hierarchy.dart';
@@ -171,8 +172,7 @@ MockSubtypeTester makeSubtypeTester(Map<String, List<String>> testcase) {
       }
     }
   }
-  var program = new Program(libraries: [environment.dummyLibrary]);
-  var hierarchy = new ClassHierarchy(program);
+  var hierarchy = new IncrementalClassHierarchy();
   return new MockSubtypeTester(hierarchy, objectClass.rawType,
       functionClass.rawType, futureClass, futureOrClass, environment);
 }