Assert that we don't mix K and J elements

pkg/compiler/lib/src/js_emitter/full_emitter/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.full_emitter;
 
 import 'dart:collection' show HashMap;
 import 'dart:convert';
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
@@ skipping 161 matching lines @@
 
   Emitter(this.compiler, this.namer, this._closedWorld, this.generateSourceMap,
       this.task, this._sorter)
       : classEmitter = new ClassEmitter(_closedWorld),
         interceptorEmitter = new InterceptorEmitter(_closedWorld),
         nsmEmitter = new NsmEmitter(_closedWorld) {
     constantEmitter = new ConstantEmitter(
         compiler.options,
         _closedWorld.commonElements,
         compiler.codegenWorldBuilder,
-        compiler.backend.rtiNeed,
+        _closedWorld.rtiNeed,
         compiler.backend.rtiEncoder,
         namer,
         task,
         this.constantReference,
         constantListGenerator);
     containerBuilder.emitter = this;
     classEmitter.emitter = this;
     nsmEmitter.emitter = this;
     interceptorEmitter.emitter = this;
   }
@@ skipping 1771 matching lines @@
     // data.
     mapping["_comment"] = "This mapping shows which compiled `.js` files are "
         "needed for a given deferred library import.";
     mapping.addAll(compiler.deferredLoadTask.computeDeferredMap());
     compiler.outputProvider(
         compiler.options.deferredMapUri.path, '', OutputType.info)
       ..add(const JsonEncoder.withIndent("  ").convert(mapping))
       ..close();
   }
 }