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

pkg/kernel/test/treeshaker_check.dart

Index: pkg/kernel/test/treeshaker_check.dart
diff --git a/pkg/kernel/test/treeshaker_check.dart b/pkg/kernel/test/treeshaker_check.dart
index 8abb640803060f12d99d3409944f2c69ade7688f..32de08f062d3f55fbda105f6a6d39e57ec075ac3 100644
--- a/pkg/kernel/test/treeshaker_check.dart
+++ b/pkg/kernel/test/treeshaker_check.dart
@@ -3,6 +3,7 @@
 // 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';
@@ -19,7 +20,8 @@ main(List<String> args) {
     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);
 }