Don't recreate CoreTypes in transformers. Pass it in.

pkg/kernel/test/treeshaker_check.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_check;
 
+import 'package:kernel/core_types.dart';
 import 'package:kernel/kernel.dart';
 import 'package:kernel/transformations/treeshaker.dart';
 import 'dart:io';
 
 String usage = '''
 Usage: treeshaker_check FILE.dill
 
 Run the tree shaker on FILE.dill and perform some internal sanity checks.
 ''';
 
 main(List<String> args) {
   if (args.length == 0) {
     print(usage);
     exit(1);
   }
   var program = loadProgramFromBinary(args[0]);
-  var shaker = new TreeShaker(program);
+  var coreTypes = new CoreTypes(program);
+  var shaker = new TreeShaker(coreTypes, program);
   shaker.transform(program);
   new TreeShakingSanityCheck(shaker).visit(program);
 }
 
 class TreeShakingSanityCheck extends RecursiveVisitor {
   final TreeShaker shaker;
   bool isInCoreLibrary = false;
 
   TreeShakingSanityCheck(this.shaker);
 
@@ skipping 13 matching lines @@
       throw 'Unused member $member was not removed';
     }
   }
 
   defaultMemberReference(Member target) {
     if (!shaker.isMemberUsed(target)) {
       throw 'Found reference to $target';
     }
   }
 }