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

pkg/kernel/test/closures/suite.dart

 // Copyright (c) 2017, 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.md file.
 
 library test.kernel.closures.suite;
 
 import 'dart:async' show Future;
 
 import 'package:front_end/physical_file_system.dart' show PhysicalFileSystem;
 
+import 'package:kernel/core_types.dart' show CoreTypes;
+
 import 'package:testing/testing.dart'
     show Chain, ChainContext, Result, Step, TestDescription, runMe;
 
 import 'package:front_end/src/fasta/testing/patched_sdk_location.dart'
     show computePatchedSdk;
 
 import 'package:kernel/ast.dart' show Program;
 
 import 'package:kernel/transformations/closure_conversion.dart'
     as closure_conversion;
@@ skipping 97 matching lines @@
 
 class ClosureConversion
     extends Step<Program, Program, ClosureConversionContext> {
   const ClosureConversion();
 
   String get name => "closure conversion";
 
   Future<Result<Program>> run(
       Program program, ClosureConversionContext testContext) async {
     try {
-      program = closure_conversion.transformProgram(program);
+      CoreTypes coreTypes = new CoreTypes(program);
+      program = closure_conversion.transformProgram(coreTypes, program);
       return pass(program);
     } catch (e, s) {
       return crash(e, s);
     }
   }
 }
 
 main(List<String> arguments) => runMe(arguments, createContext, "testing.json");