Remove support for attribute event listeners.

client/fling/dist/runtime/apps/adminz/adminz.dart

 // Copyright (c) 2011, 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.
 
 typedef void XhrCallback(XMLHttpRequest xhr);
 
 class Xhr {
   static void post(Window window, String url, String data, String contentType,
       XhrCallback onSuccess, XhrCallback onFailure) {
     _request(window, 'POST', url, data, contentType, onSuccess, onFailure);
   }
 
   static void _request(Window window, String method, String url, String data,
       String contentType, XhrCallback onSuccess, XhrCallback onFailure) {
     // TODO(knorton): Catch exceptions.
     final xhr = new XMLHttpRequest();
-    xhr.onreadystatechange = () {
+    final onReadyStateChange = () {
       if (xhr.readyState != 4)
         return;
 
-      xhr.onreadystatechange = null;
+      xhr.removeEventListener('readystatechange', onReadyStateChange);
       if (xhr.status == 200) {
         if (onSuccess != null)
           onSuccess(xhr);
       } else {
         if (onFailure != null)
           onFailure(xhr);
       }
     };
+    xhr.addEventListener('readystatechange', onReadyStateChange, true);
     xhr.open(method, url, true);
     if (contentType == null) {
       xhr.setRequestHeader('Content-Type', contentType);
     }
     // TODO(knorton): This is a problem with dart_dom bindings. A fix will arrive
     // soon.
     // xhr.send(data);
     xhr.send(null);
   }
 }
@@ skipping 93 matching lines @@
         return src.substring(0, src.length - name.length);
     }
     window.console.warn('Adminz was unable find itself in the DOM :-(');
     return null;
   }
 
   static void main() {
     Adminz.attach(window, window.document);
   }
 }