dart2js: Not all interceptor accesses are safe.

pkg/compiler/lib/src/js_emitter/new_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.new_js_emitter.emitter;
 
 import '../program_builder.dart' show ProgramBuilder;
 import '../model.dart';
 import 'model_emitter.dart';
 import '../../common.dart';
@@ skipping 110 matching lines @@
 
   @override
   js.PropertyAccess prototypeAccess(ClassElement element,
                                     bool hasBeenInstantiated) {
     js.Expression constructor =
         hasBeenInstantiated ? constructorAccess(element) : typeAccess(element);
     return js.js('#.prototype', constructor);
   }
 
   @override
-  js.PropertyAccess interceptorClassAccess(ClassElement element) {
-    // Interceptors are eagerly constructed. It's safe to just access them.
-    return _globalPropertyAccess(element);
+  js.Expression interceptorClassAccess(ClassElement element) {
+    // Some interceptors are eagerly constructed. However, native interceptors
+    // aren't.
+    return js.js('#.ensureResolved()', _globalPropertyAccess(element));
   }
 
   @override
   js.Expression typeAccess(Element element) {
     // TODO(floitsch): minify 'ensureResolved'.
     // TODO(floitsch): don't emit `ensureResolved` for eager classes.
     return js.js('#.ensureResolved()', _globalPropertyAccess(element));
   }
 
   @override
   void invalidateCaches() {}
 }