Remove ClassHierarchy factory constructor.

pkg/kernel/lib/class_hierarchy.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.class_hierarchy;
 
 import 'ast.dart';
 import 'dart:math';
 import 'dart:typed_data';
 import 'src/heap.dart';
 import 'type_algebra.dart';
 
 /// Interface for answering various subclassing queries.
 /// TODO(scheglov) Several methods are not used, or used only in tests.
 /// Check if these methods are not useful and should be removed .
 abstract class ClassHierarchy {
-  factory ClassHierarchy(Program program) =>
-      new ClosedWorldClassHierarchy(program);
-
   /// Given the [unordered] classes, return them in such order that classes
   /// occur after their superclasses.  If some superclasses are not in
   /// [unordered], they are not included.
   Iterable<Class> getOrderedClasses(Iterable<Class> unordered);
 
   /// Returns the unique index of the [class_].
   int getClassIndex(Class class_);
 
   /// True if the program contains another class that is a subtype of given one.
   bool hasProperSubtypes(Class class_);
@@ skipping 1104 matching lines @@
 class _LubHeap extends Heap<_ClassInfo> {
   @override
   bool sortsBefore(_ClassInfo a, _ClassInfo b) => sortsBeforeStatic(a, b);
 
   static bool sortsBeforeStatic(_ClassInfo a, _ClassInfo b) {
     if (a.depth > b.depth) return true;
     if (a.depth < b.depth) return false;
     return a.topologicalIndex < b.topologicalIndex;
   }
 }