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

pkg/front_end/lib/src/fasta/kernel/kernel_outline_shaker.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.
 
 /// A transformation to create a self-contained modular kernel without
 /// unnecessary references to other libraries.
 library fasta.kernel.kernel_outline_shaker;
 
 import 'package:kernel/ast.dart';
 import 'package:kernel/core_types.dart';
@@ skipping 144 matching lines @@
 }
 
 /// Determines the root APIs that need to be retained before running the
 /// tree-shaker.
 ///
 /// This is implemented using a visitor that walks through the sources that are
 /// intended to be part of the kernel output.
 // TODO(sigmund): delete. We should collect this information while
 // building kernel without having to run a visitor afterwards.
 class RootsMarker extends RecursiveVisitor {
+  final CoreTypes coreTypes;
   final RetainedDataBuilder data;
-  RootsMarker(this.data);
+
+  RootsMarker(this.coreTypes, this.data);
 
   void run(Program program, bool isIncluded(Uri uri)) {
     markRequired(program);
     data.markMember(program.mainMethod);
     for (var library in program.libraries) {
       if (isIncluded(library.importUri)) {
         library.accept(this);
       }
     }
   }
 
   /// Marks classes and members that are assumed to exist by fasta or by
   /// transformers.
   // TODO(sigmund): consider being more fine-grained and only marking what is
   // seen and used.
   void markRequired(Program program) {
-    var coreTypes = new CoreTypes(program);
     coreTypes.objectClass.members.forEach(data.markMember);
 
     // These are assumed to be available by fasta:
     data.markClass(coreTypes.objectClass);
     data.markClass(coreTypes.nullClass);
     data.markClass(coreTypes.boolClass);
     data.markClass(coreTypes.intClass);
     data.markClass(coreTypes.numClass);
     data.markClass(coreTypes.doubleClass);
     data.markClass(coreTypes.stringClass);
@@ skipping 200 matching lines @@
   /// Types appear to be encoded directly, so we have no need to preserve
   /// typedefs.
   // TODO(sigmund): revisit if this is not the case, the `inputError` in
   // [RootsMarker] is meant to detect this.
   Typedef visitTypedef(Typedef node) => null;
 
   TreeNode defaultTreeNode(TreeNode node) => node;
 }
 
 typedef bool Filter(Uri uri);