Support serialization of WorldImpact

pkg/compiler/lib/src/js_backend/field_naming_mixin.dart

Index: pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
diff --git a/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart b/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
index 0a89b42c528461f7a019af081a0d18eec51064c4..c821aeaf98a1326b99f19af798a46071610bd459 100644
--- a/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
+++ b/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
@@ -14,8 +14,9 @@ abstract class _MinifiedFieldNamer implements Namer {
   // this could be because the field belongs to a mixin. In such a case this
   // will return `null` and a normal field name has to be used.
   jsAst.Name _minifiedInstanceFieldPropertyName(Element element) {
-    if (backend.hasFixedBackendName(element)) {
-      return new StringBackedName(backend.getFixedBackendName(element));
+    if (backend.nativeData.hasFixedBackendName(element)) {
+      return new StringBackedName(
+          backend.nativeData.getFixedBackendName(element));
     }
 
     _FieldNamingScope names;