Assert that we don't mix K and J elements

pkg/compiler/lib/src/js_backend/js_interop_analysis.dart

 // Copyright (c) 2015, 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.
 
 /// Analysis to determine how to generate code for typed JavaScript interop.
 library compiler.src.js_backend.js_interop_analysis;
 
 import '../elements/resolution_types.dart'
     show ResolutionDartType, ResolutionDynamicType, ResolutionFunctionType;
 import '../js/js.dart' as jsAst;
 import '../js/js.dart' show js;
 import '../universe/selector.dart' show Selector;
 import '../universe/world_builder.dart' show SelectorConstraints;
 import 'js_backend.dart' show JavaScriptBackend;
 
 class JsInteropAnalysis {
   final JavaScriptBackend backend;
 
   JsInteropAnalysis(this.backend);
 
   jsAst.Statement buildJsInteropBootstrap() {
-    if (!backend.nativeBasicData.isJsInteropUsed) return null;
+    if (!backend.compiler.frontendStrategy.nativeBasicData.isJsInteropUsed)
+      return null;
     List<jsAst.Statement> statements = <jsAst.Statement>[];
     backend.compiler.codegenWorldBuilder.forEachInvokedName(
         (String name, Map<Selector, SelectorConstraints> selectors) {
       selectors.forEach((Selector selector, SelectorConstraints constraints) {
         if (selector.isClosureCall) {
           // TODO(jacobr): support named arguments.
           if (selector.namedArgumentCount > 0) return;
           int argumentCount = selector.argumentCount;
           var candidateParameterNames =
               'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
@@ skipping 13 matching lines @@
   ResolutionFunctionType buildJsFunctionType() {
     // TODO(jacobr): consider using codegenWorldBuilder.isChecks to determine the
     // range of positional arguments that need to be supported by JavaScript
     // function types.
     return new ResolutionFunctionType.synthesized(
         const ResolutionDynamicType(),
         [],
         new List<ResolutionDartType>.filled(16, const ResolutionDynamicType()));
   }
 }