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

pkg/compiler/lib/src/js_emitter/old_emitter/class_emitter.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;
 
 class ClassEmitter extends CodeEmitterHelper {
 
   ClassStubGenerator get _stubGenerator =>
       new ClassStubGenerator(compiler, namer, backend);
 
   /**
    * Documentation wanted -- johnniwinther
    */
   void emitClass(Class cls,
                  ClassBuilder enclosingBuilder,
                  Map<String, jsAst.Expression> additionalProperties) {
     ClassElement classElement = cls.element;
 
     assert(invariant(classElement, classElement.isDeclaration));
-    assert(invariant(classElement, !cls.isNative || cls.onlyForRti));
 
     emitter.needsClassSupport = true;
 
     ClassElement superclass = classElement.superclass;
     String superName = "";
     if (superclass != null) {
       superName = namer.getNameOfClass(superclass);
     }
 
     if (cls.isMixinApplication) {
@@ skipping 555 matching lines @@
               js.number(index));
     }
     jsAst.Expression convertRtiToRuntimeType = emitter
         .staticFunctionAccess(backend.findHelper('convertRtiToRuntimeType'));
     compiler.dumpInfoTask.registerElementAst(element,
         builder.addProperty(name,
             js('function () { return #(#) }',
                 [convertRtiToRuntimeType, computeTypeVariable])));
   }
 }