Sample test for custom elements.

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index e33d421417b5c54dbd7df861804c9c92101fb578..fcc0041d96512ce77446d3a0041adbfcb95f758a 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -8822,6 +8822,12 @@ abstract class Element extends Node implements ElementTraversal native "*Element
     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
@@ -12549,6 +12555,17 @@ class HtmlDocument extends Document native "*HTMLDocument" {
     document.$dom_body = value;
   }
 
+  /**
+   * Registers a custom Element subclass as an available HTML tag.
+   *
+   * Not yet implemented.
+   */
+  @Experimental
+  void register(String tagName, Type elementClass) {
+    // TODO: tagName validation
+    throw new Exception('Not yet implemented');
+  }
+
   @DomName('Document.caretRangeFromPoint')
   Range caretRangeFromPoint(int x, int y) {
     return document.$dom_caretRangeFromPoint(x, y);
@@ -26063,7 +26080,7 @@ class WebKitNamedFlow extends EventTarget native "*WebKitNamedFlow" {
 
 @DocsEditable
 @DomName('WebKitTransitionEvent')
-class WebKitTransitionEvent extends Event native "*WebKitTransitionEvent" {
+class WebKitTransitionEvent implements TransitionEvent  native "*WebKitTransitionEvent" {
 
   @DomName('WebKitTransitionEvent.elapsedTime')
   @DocsEditable