Sample test for custom elements.

tools/dom/templates/html/impl/impl_Element.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.
 
 part of $LIBRARYNAME;
 
 // TODO(jacobr): use _Lists.dart to remove some of the duplicated
 // functionality.
 class _ChildrenElementList implements List {
   // Raw Element.
@@ skipping 735 matching lines @@
   /**
    * Checks to see if the tag name is supported by the current platform.
    *
    * The tag should be a valid HTML tag name.
    */
   static bool isTagSupported(String tag) {
     var e = _ElementFactoryProvider.createElement_tag(tag);
     return e is Element && !(e is UnknownElement);
   }
 
+  /**
+   * Called by the DOM when this element has been instantiated.
+   */
+  @Experimental
+  void onCreated() {}
+
   // Hooks to support custom WebComponents.
   /**
    * Experimental support for [web components][wc]. This field stores a
    * reference to the component implementation. It was inspired by Mozilla's
    * [x-tags][] project. Please note: in the future it may be possible to
    * `extend Element` from your class, in which case this field will be
    * deprecated and will simply return this [Element] object.
    *
    * [wc]: http://dvcs.w3.org/hg/webcomponents/raw-file/tip/explainer/index.html
    * [x-tags]: http://x-tags.org/
@@ skipping 270 matching lines @@
   // Optimization to improve performance until the dart2js compiler inlines this
   // method.
   static dynamic createElement_tag(String tag) =>
       // Firefox may return a JS function for some types (Embed, Object).
       JS('Element|=Object', 'document.createElement(#)', tag);
 $else
   static Element createElement_tag(String tag) =>
       document.$dom_createElement(tag);
 $endif
 }