dart:html perf optimization based on runing Dromaeo benchmarks

lib/dom/templates/html/frog/impl_EventTarget.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.
 
 class _EventsImpl implements Events {
   /* Raw event target. */
   // TODO(jacobr): it would be nice if we could specify this as
   // _EventTargetImpl or EventTarget
   final var _ptr;
 
@@ skipping 25 matching lines @@
   _EventListenerListImpl remove(EventListener listener,
       [bool useCapture = false]) {
     _remove(listener, useCapture);
     return this;
   }
 
   bool dispatch(Event evt) {
     // TODO(jacobr): what is the correct behavior here. We could alternately
     // force the event to have the expected type.
     assert(evt.type == _type);
-    return _ptr._dispatchEvent(evt);
+    return _ptr.$dom_dispatchEvent(evt);
   }
 
   void _add(EventListener listener, bool useCapture) {
-    _ptr._addEventListener(_type, listener, useCapture);
+    _ptr.$dom_addEventListener(_type, listener, useCapture);
   }
 
   void _remove(EventListener listener, bool useCapture) {
-    _ptr._removeEventListener(_type, listener, useCapture);
+    _ptr.$dom_removeEventListener(_type, listener, useCapture);
   }
 }
 
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
   Events get on() => new _EventsImpl(this);
 $!MEMBERS
 }