end_to_end_test detects errors instead of timing out.

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
 /// test just waits for a "Hello, World!" message.
 library trydart.end_to_end_test;
 
 import 'dart:html';
 import 'dart:async';
 
+// TODO(ahe): Remove this import if issue 17936 is fixed.
+import 'dart:js' as hack;
+
 import 'package:async_helper/async_helper.dart';
 
+void installErrorHandlerOn(IFrameElement iframe) {
+  // This method uses dart:js to install an error event handler on the content
+  // window of [iframe]. This is a workaround for http://dartbug.com/17936.
+  var iframeProxy = new hack.JsObject.fromBrowserObject(iframe);
+  var contentWindowProxy = iframeProxy['contentWindow'];
+  if (contentWindowProxy == null) return;

[kustermann, 2014/04/01 20:27:30]

If contentWindowProxy is null, we should fail, otherwise the test will
eventually time out, right?

[and we don't like tests to time out]

[ahe, 2014/04/01 21:21:17]

I can't tell when contentWindowProxy is null. As far as I can gather:

* contentWindowProxy is always null before you add the iframe to the document.

* contentWindowProxy is null if iframe.src is a different origin.

However, it isn't clear from the documentation, so I'm trying to be robust.

I'll sleep on this.

[ahe, 2014/04/03 11:05:35]

Changed it to throw an exception.

+  contentWindowProxy.callMethod('addEventListener', ['error', (eventProxy) {
+    String filename = eventProxy['filename'];
+    int lineno = eventProxy['lineno'];
+    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) {
+  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();
 
       // Clean up after ourselves.
       window.localStorage.clear();
 
       asyncSuccess(null);
     } else {
       window.console.dir(e.data);
     }
   });
 
   // Clearing localStorage makes Try Dart! think it is opening for the first
   // time.
   window.localStorage.clear();
 
-  document.body.append(new IFrameElement()
+  IFrameElement iframe = new IFrameElement()
       ..src = '/root_build/try_dartlang_org/index.html'
       ..style.width = '90vw'
-      ..style.height = '90vh');
+      ..style.height = '90vh'
+      ..onLoad.listen(onIframeLoaded);
+  document.body.append(iframe);
+  installErrorHandlerOn(iframe);

[kustermann, 2014/04/01 20:27:30]

Why are you doing this here and in the onIframeLoaded function?

[ahe, 2014/04/01 21:21:17]

As far as I can gather, it matters. I think there are two different
contentWindows, depending on how far the browser has gotten. It's really hard to
find proper documentation about this.

I'll add some comments.

 }