Assert that we don't mix K and J elements

pkg/compiler/lib/src/ssa/graph_builder.dart

 // Copyright (c) 2016, 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.
 
 import '../closure.dart' show ClosureDataLookup;
 import '../constants/constant_system.dart';
 import '../common/codegen.dart' show CodegenRegistry;
 import '../common_elements.dart';
 import '../compiler.dart';
 import '../deferred_load.dart';
@@ skipping 65 matching lines @@
       compiler.backendStrategy.closureDataLookup;
 
   NativeData get nativeData => closedWorld.nativeData;
 
   InterceptorData get interceptorData => closedWorld.interceptorData;
 
   BackendUsage get backendUsage => closedWorld.backendUsage;
 
   Namer get namer => backend.namer;
 
-  RuntimeTypesNeed get rtiNeed => backend.rtiNeed;
+  RuntimeTypesNeed get rtiNeed => closedWorld.rtiNeed;
 
   JavaScriptConstantCompiler get constants => backend.constants;
 
   ConstantSystem get constantSystem => constants.constantSystem;
 
   RuntimeTypesEncoder get rtiEncoder => backend.rtiEncoder;
 
   FunctionInlineCache get inlineCache => backend.inlineCache;
 
   MirrorsData get mirrorsData => backend.mirrorsData;
@@ skipping 201 matching lines @@
         return mirrorsData.mustRetainMetadata;
       case 'USE_CONTENT_SECURITY_POLICY':
         return options.useContentSecurityPolicy;
       case 'IS_FULL_EMITTER':
         return !USE_LAZY_EMITTER && !options.useStartupEmitter;
       default:
         return null;
     }
   }
 }