Fix unknownelement_test after recent rework.

tests/html/html.status

 # 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.
 
 event_test: Skip  # Issue 1996
 webgl_1_test: Skip  # Issue 1495
 xmldocument_test: Skip  # XML in dart:html is incomplete
 xmlelement_test: Skip  # XML in dart:html is incomplete
 measurement_test: Pass, Fail  # Issue 1940
 
 [ $runtime == drt ]
 xhr_cross_origin_test: Skip  # Issue 4502: Passes with --allow-external-pages.
 
 [ $compiler == none && ($runtime == drt || $runtime == dartium) ]
 request_animation_frame_test: Skip   # drt hangs; requestAnimationFrame not implemented
 url_test: Fail   # createObjectURL not implemented.
-unknownelement_test: Fail # In work by antonm.
 
 [ $compiler == none && $runtime == drt && $system == windows]
 audiocontext_test: Skip
 
 [ $compiler == none && ($runtime == drt || $runtime == dartium) && $system == windows]
 websql_test: Skip # Issue 4941: stderr contains a backtrace.
 
 [ $compiler == none && ($runtime == drt || $runtime == dartium) && $mode == debug]
 websql_test: Fail, Pass # Issue 4941: stderr contains a backtrace.
 
@@ skipping 168 matching lines @@
 [ $compiler == dart2js && $runtime == chrome && $system == windows]
 css_test: Pass, Fail # Issue #2823
 
 [ $compiler == dart2js && $runtime == ff && $system == windows]
 js_interop_2_test: Fail # Issue 4658.
 
 [ $compiler == dart2js && $checked && $browser]
 fileapi_test: Fail # TypeError: Object #<DirectoryEntry> has no method 'get$name'
 cross_frame_test: Fail # Caught NoSuchMethodError : method not found: 'is$_WindowImpl'
 window_open_test: Fail # Caught NoSuchMethodError : method not found: 'is$_WindowImpl'