Support user generated custom native JS classes.

pkg/compiler/lib/src/serialization/modelz.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.
 
 /// Implementation of the element model used for deserialiation.
 ///
 /// These classes are created by [ElementDeserializer] triggered by the
 /// [Deserializer].
 
 library dart2js.serialization.modelz;
@@ skipping 127 matching lines @@
   @override
   bool get isLocal => false;
 
   @override
   bool get isMixinApplication => false;
 
   @override
   bool get isNative => false;
 
   @override
+  bool get isJsInterop => false;
+
+  @override
   bool get isOperator => false;
 
   @override
   bool get isStatic => false;
 
   // TODO(johnniwinther): Find a more precise semantics for this.
   @override
   bool get isSynthesized => true;
 
   @override
@@ skipping 1311 matching lines @@
 
   @override
   accept(ElementVisitor visitor, arg) {
     return visitor.visitFieldParameterElement(this, arg);
   }
 
   @override
   ElementKind get kind => ElementKind.INITIALIZING_FORMAL;
 
 }