spawnDomUri stub for dart2js

tools/dom/templates/html/dart2js/html_dart2js.darttemplate

 // 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.
 
 // DO NOT EDIT - unless you are editing documentation as per:
 // https://code.google.com/p/dart/wiki/ContributingHTMLDocumentation
 // Auto-generated dart:html library.
 
 /**
  * HTML elements and other resources for web-based applications that need to
@@ skipping 114 matching lines @@
    *
    * This can only be called by subclasses from their created constructor.
    */
   HtmlElement.created() : super.created();
 }
 
 // EntryArray type was removed, so explicitly adding it to allow support for
 // older Chrome versions.
 // Issue #12573.
 abstract class _EntryArray implements List<Entry> native "EntryArray" {}
+
+/**
+ * Spawn a DOM isolate using the given URI in the same window.
+ * This isolate is not concurrent.  It runs on the browser thread
+ * with full access to the DOM.
+ * Note: this API is still evolving and may move to dart:isolate.
+ */
+@Experimental()
+Future<Isolate> spawnDomUri(Uri uri, List<String> args, message) {
+  // TODO(17738): Implement this.
+  throw new UnimplementedError();
+}