Pass ClassHierarchy instead of creating it.

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 40 matching lines @@
     return options['basic']
         ? new BasicClassHierarchy(program)
         : new ClassHierarchy(program);
   }
 
   CoreTypes coreTypes = new CoreTypes(program);
 
   var watch = new Stopwatch()..start();
   ClassHierarchy sharedClassHierarchy = buildClassHierarchy();
   int coldHierarchyTime = watch.elapsedMicroseconds;
-  var shaker = new TreeShaker(coreTypes, program,
-      hierarchy: sharedClassHierarchy, strongMode: strongMode);
+  var shaker = new TreeShaker(coreTypes, sharedClassHierarchy, program,
+      strongMode: strongMode);
   if (options['diagnose']) {
     print(shaker.getDiagnosticString());
   }
   shaker = null;
   int coldTreeShakingTime = watch.elapsedMicroseconds;
 
   ClassHierarchy getClassHierarchy() {
     return options['from-scratch']
         ? buildClassHierarchy()
         : sharedClassHierarchy;
   }
 
   const int numberOfTrials = 50;
   int hotHierarchyTime = 0;
   int hotTreeShakingTime = 0;
   watch.reset();
   for (int i = 0; i < numberOfTrials; i++) {
     watch.reset();
     var hierarchy = getClassHierarchy();
     hotHierarchyTime += watch.elapsedMicroseconds;
-    new TreeShaker(coreTypes, program,
-        hierarchy: hierarchy, strongMode: strongMode);
+    new TreeShaker(coreTypes, hierarchy, program, strongMode: strongMode);
     hotTreeShakingTime += watch.elapsedMicroseconds;
   }
   hotHierarchyTime ~/= numberOfTrials;
   hotTreeShakingTime ~/= numberOfTrials;
 
   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)''');
 }