Assert that we don't mix K and J elements

pkg/compiler/lib/src/js_emitter/lazy_emitter/model_emitter.dart

 // Copyright (c) 2014, 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.
 
 library dart2js.js_emitter.lazy_emitter.model_emitter;
 
 import 'package:js_runtime/shared/embedded_names.dart'
     show
         CREATE_NEW_ISOLATE,
         DEFERRED_LIBRARY_URIS,
@@ skipping 41 matching lines @@
   static const String deferredExtension = "part.js";
 
   static const String typeNameProperty = r"builtin$cls";
 
   ModelEmitter(this.compiler, this.namer, this.nativeEmitter, this._closedWorld,
       CodeEmitterTask task) {
     this.constantEmitter = new ConstantEmitter(
         compiler.options,
         _closedWorld.commonElements,
         compiler.codegenWorldBuilder,
-        compiler.backend.rtiNeed,
+        _closedWorld.rtiNeed,
         compiler.backend.rtiEncoder,
         namer,
         task,
         this.generateConstantReference,
         constantListGenerator);
   }
 
   InterceptorData get _interceptorData => _closedWorld.interceptorData;
 
   js.Expression constantListGenerator(js.Expression array) {
@@ skipping 1215 matching lines @@
   #eagerClasses;
 
   var end = Date.now();
   // print('Setup: ' + (end - start) + ' ms.');
 
   #invokeMain;  // Start main.
 
 })(Date.now(), #code)
 }""";
 }