Pass ClassHierarchy instead of creating it.

pkg/kernel/test/treeshaker_membench.dart

Index: pkg/kernel/test/treeshaker_membench.dart
diff --git a/pkg/kernel/test/treeshaker_membench.dart b/pkg/kernel/test/treeshaker_membench.dart
index 8147445034d8af79e378e4eff95ea53c5adf17a6..8ca99eaca9289afa7157d2fa8247436301d81cf3 100644
--- a/pkg/kernel/test/treeshaker_membench.dart
+++ b/pkg/kernel/test/treeshaker_membench.dart
@@ -45,8 +45,8 @@ main(List<String> args) {
   int copyCount = int.parse(options['count']);
 
   TreeShaker buildTreeShaker() {
-    return new TreeShaker(coreTypes, program,
-        hierarchy: hierarchy, strongMode: strongMode);
+    return new TreeShaker(coreTypes, hierarchy, program,
+        strongMode: strongMode);
   }
 
   List<TreeShaker> keepAlive = <TreeShaker>[];