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

pkg/kernel/test/treeshaker_dump.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_dump;
 
 import 'dart:io';
+import 'package:kernel/core_types.dart';
 import 'package:kernel/kernel.dart';
 import 'package:kernel/transformations/treeshaker.dart';
 import 'package:args/args.dart';
 import 'package:path/path.dart' as pathlib;
 import 'package:kernel/text/ast_to_text.dart';
 
 ArgParser parser = new ArgParser(allowTrailingOptions: true)
   ..addFlag('used', help: 'Print used members', negatable: false)
   ..addFlag('unused', help: 'Print unused members', negatable: false)
   ..addFlag('instantiated',
@@ skipping 40 matching lines @@
   String filename = options.rest.single;
 
   if (options['output'] != null && !options['diff']) {
     print('--output must be used with --diff');
     exit(1);
   }
 
   bool strong = options['strong'];
 
   Program program = loadProgramFromBinary(filename);
-  TreeShaker shaker = new TreeShaker(program, strongMode: strong);
+  CoreTypes coreTypes = new CoreTypes(program);
+  TreeShaker shaker = new TreeShaker(coreTypes, program, strongMode: strong);
   int totalClasses = 0;
   int totalInstantiationCandidates = 0;
   int totalMembers = 0;
   int usedClasses = 0;
   int instantiatedClasses = 0;
   int usedMembers = 0;
 
   void visitMember(Member member) {
     if (member.isAbstract) return; // Abstract members are not relevant.
     ++totalMembers;
@@ skipping 42 matching lines @@
 
   if (options['diff']) {
     String name = pathlib.basenameWithoutExtension(filename);
     String outputDir = options['output'] ?? '';
     String beforeFile = pathlib.join(outputDir, '$name.before.txt');
     String afterFile = pathlib.join(outputDir, '$name.after.txt');
     NameSystem names = new NameSystem();
     StringBuffer before = new StringBuffer();
     new Printer(before, syntheticNames: names).writeProgramFile(program);
     new File(beforeFile).writeAsStringSync('$before');
-    new TreeShaker(program, strongMode: strong).transform(program);
+    new TreeShaker(coreTypes, program, strongMode: strong).transform(program);
     StringBuffer after = new StringBuffer();
     new Printer(after, syntheticNames: names).writeProgramFile(program);
     new File(afterFile).writeAsStringSync('$after');
     print('Text written to $beforeFile and $afterFile');
   }
 }
 
 String ratio(num x, num total) {
   return '$x / $total (${percent(x, total)})';
 }
 
 String percent(num x, num total) {
   return total == 0 ? '0%' : ((100 * x / total).toStringAsFixed(0) + '%');
 }