Fix checked-mode problem

dart/tests/try/end_to_end_test.dart

 // Copyright (c) 2014, 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.
 
 /// Whitebox integration/end-to-end test of Try Dart! site.
 ///
 /// This test opens Try Dart! in an iframe.  When opened the first time, Try
 /// Dart! will display a simple hello-world example, color tokens, compile the
 /// example, and run the result.  We've instrumented Try Dart! to use
 /// window.parent.postMessage when the running program prints anything. So this
@@ skipping 23 matching lines @@
     String message = eventProxy['message'];
     print("Error occurred in iframe: $message");
     new Future(() {
       // Chrome seems to not call window.onerror when you throw in response to
       // an error event. So we throw the error in a future.
       throw 'Error from iframe: $filename:$lineno: $message';
     });
   }]);
 }
 
-void onIframeLoaded(ErrorEvent event) {
+void onIframeLoaded(Event event) {
   installErrorHandlerOn(event.target);
 }
 
 void main() {
   asyncStart();
   window.onMessage.listen((MessageEvent e) {
     if (e.data == 'Hello, World!\n') {
       // Clear the DOM to work around a bug in test.dart.
       document.body.nodes.clear();
 
@@ skipping 14 matching lines @@
       ..src = '/root_build/try_dartlang_org/index.html'
       ..style.width = '90vw'
       ..style.height = '90vh'
       ..onLoad.listen(onIframeLoaded);
   document.body.append(iframe);
   // Install an error handler both on the new iframe element, and when it has
   // fired the load event.  That seems to matter according to some sources on
   // stackoverflow.
   installErrorHandlerOn(iframe);
 }