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

pkg/kernel/test/treeshaker_bench.dart

Index: pkg/kernel/test/treeshaker_bench.dart
diff --git a/pkg/kernel/test/treeshaker_bench.dart b/pkg/kernel/test/treeshaker_bench.dart
index 7a83c7a4aa2c4cc215284d0acd1a3cab83ef45f3..3b2fd090cc4f08cac61ba73c6005c9c74daba75c 100644
--- a/pkg/kernel/test/treeshaker_bench.dart
+++ b/pkg/kernel/test/treeshaker_bench.dart
@@ -58,10 +58,8 @@ void main(List<String> args) {
   var watch = new Stopwatch()..start();
   ClassHierarchy sharedClassHierarchy = buildClassHierarchy();
   int coldHierarchyTime = watch.elapsedMicroseconds;
-  var shaker = new TreeShaker(program,
-      hierarchy: sharedClassHierarchy,
-      coreTypes: coreTypes,
-      strongMode: strongMode);
+  var shaker = new TreeShaker(coreTypes, program,
+      hierarchy: sharedClassHierarchy, strongMode: strongMode);
   if (options['diagnose']) {
     print(shaker.getDiagnosticString());
   }
@@ -82,8 +80,8 @@ void main(List<String> args) {
     watch.reset();
     var hierarchy = getClassHierarchy();
     hotHierarchyTime += watch.elapsedMicroseconds;
-    new TreeShaker(program,
-        hierarchy: hierarchy, coreTypes: coreTypes, strongMode: strongMode);
+    new TreeShaker(coreTypes, program,
+        hierarchy: hierarchy, strongMode: strongMode);
     hotTreeShakingTime += watch.elapsedMicroseconds;
   }
   hotHierarchyTime ~/= numberOfTrials;