Add touchenter event even though it doesn't have an ontouchenter method in the DOM.

lib/html/dartium/html_dartium.dart

Index: lib/html/dartium/html_dartium.dart
diff --git a/lib/html/dartium/html_dartium.dart b/lib/html/dartium/html_dartium.dart
index 63c7b5e9c57764f93f4c32d86932d349add3d829..6d500b7045cd07b44ac536790b68da3e2efade84 100644
--- a/lib/html/dartium/html_dartium.dart
+++ b/lib/html/dartium/html_dartium.dart
@@ -8542,6 +8542,8 @@ class _ElementEventsImpl extends _EventsImpl implements ElementEvents {
 
   EventListenerList get touchEnd() => _get('touchend');
 
+  EventListenerList get touchEnter() => _get('touchenter');
+
   EventListenerList get touchLeave() => _get('touchleave');
 
   EventListenerList get touchMove() => _get('touchmove');
@@ -27036,6 +27038,8 @@ interface ElementEvents extends Events {
 
   EventListenerList get touchEnd();
 
+  EventListenerList get touchEnter();
+
   EventListenerList get touchLeave();
 
   EventListenerList get touchMove();