A type for unsupported browser objects

tools/dom/src/html_native_DOMImplementation.dart

 // Copyright (c) 2012, 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.
 
 part of html;
 
 class _Property {
   _Property(this.name) :
       _hasValue = false,
       writable = false,
@@ skipping 972 matching lines @@
   _scheduleImmediateHelper._schedule(callback);
 };
 
 get _pureIsolateScheduleImmediateClosure => ((void callback()) =>
   throw new UnimplementedError("scheduleMicrotask in background isolates "
                                "are not supported in the browser"));
 
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }
+
+// Class for unsupported native browser 'DOM' objects.
+class _UnsupportedBrowserObject extends NativeFieldWrapperClass2 {
+}