Pass ClassHierarchy instead of creating it.

pkg/front_end/lib/src/fasta/source/source_loader.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 fasta.source_loader;
 
 import 'dart:async' show Future;
 
 import 'dart:typed_data' show Uint8List;
 
 import 'package:front_end/file_system.dart';
 import 'package:front_end/src/base/instrumentation.dart' show Instrumentation;
 
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
     show KernelTypeInferenceEngine;
 
 import 'package:front_end/src/fasta/kernel/kernel_target.dart'
     show KernelTarget;
 
 import 'package:front_end/src/fasta/type_inference/type_inference_engine.dart'
     show TypeInferenceEngine;
 
 import 'package:kernel/ast.dart' show Program;
 
-import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
+import 'package:kernel/class_hierarchy.dart'
+    show ClassHierarchy, ClosedWorldClassHierarchy;
 
 import 'package:kernel/core_types.dart' show CoreTypes;
 
 import '../builder/builder.dart'
     show
         Builder,
         ClassBuilder,
         EnumBuilder,
         LibraryBuilder,
         NamedTypeBuilder,
@@ skipping 397 matching lines @@
   void buildProgram() {
     builders.forEach((Uri uri, LibraryBuilder library) {
       if (library is SourceLibraryBuilder) {
         libraries.add(library.build(coreLibrary));
       }
     });
     ticker.logMs("Built program");
   }
 
   void computeHierarchy(Program program) {
-    hierarchy = new ClassHierarchy(program);
+    hierarchy = new ClosedWorldClassHierarchy(program);
     ticker.logMs("Computed class hierarchy");
     coreTypes = new CoreTypes(program);
     ticker.logMs("Computed core types");
   }
 
   void checkOverrides(List<SourceClassBuilder> sourceClasses) {
     assert(hierarchy != null);
     for (SourceClassBuilder builder in sourceClasses) {
       builder.checkOverrides(hierarchy);
     }
@@ skipping 22 matching lines @@
   /// Performs the second phase of top level initializer inference, which is to
   /// visit fields and top level variables in topologically-sorted order and
   /// assign their types.
   void performInitializerInference() {
     typeInferenceEngine.finishTopLevel();
     ticker.logMs("Performed initializer inference");
   }
 
   List<Uri> getDependencies() => sourceBytes.keys.toList();
 }