Don't create builders to determine if a native class is trivial or not.

pkg/compiler/lib/src/js_emitter/old_emitter/class_builder.dart

 // Copyright (c) 2013, 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.
 
 part of dart2js.js_emitter;
 
 /**
  * A data structure for collecting fragments of a class definition.
  */
 class ClassBuilder {
   final List<jsAst.Property> properties = <jsAst.Property>[];
   final List<String> fields = <String>[];
 
   String superName;
   String functionType;
   List<jsAst.Node> fieldMetadata;
 
   final Element element;
   final Namer namer;
 
-  /// Set to true by user if class is indistinguishable from its superclass.
-  bool isTrivial = false;
-
   ClassBuilder(this.element, this.namer);
 
   // Has the same signature as [DefineStubFunction].
   jsAst.Property addProperty(String name, jsAst.Expression value) {
     jsAst.Property property = new jsAst.Property(js.string(name), value);
     properties.add(property);
     return property;
   }
 
   void addField(String field) {
@@ skipping 36 matching lines @@
       fieldsAndProperties.add(
           new jsAst.Property(
               js.string(namer.classDescriptorProperty), classData));
       fieldsAndProperties.addAll(properties);
     } else {
       fieldsAndProperties = properties;
     }
     return new jsAst.ObjectInitializer(fieldsAndProperties, isOneLiner: false);
   }
 }