Clear old messages when reporting exception.

dart/site/try/src/compilation.dart

 // Copyright (c) 2013, 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.
 
 library trydart.compilation;
 
 import 'dart:html' show
     Blob,
     Element,
     ErrorEvent,
@@ skipping 179 matching lines @@
     var url =
         Url.createObjectUrl(
             new Blob([codeWithPrint], 'application/javascript'));
     objectUrls.add(url);
 
     run(url, makeIframe);
   }
 
   void run(String url, IFrameElement makeIframe()) {
     void retryInIframe() {
+      interaction.aboutToRun();
       var frame = makeIframe();
       frame.style
           ..visibility = 'hidden'
           ..position = 'absolute';
       outputFrame.parent.insertBefore(frame, outputFrame);
       outputFrame = frame;
       errorStream(frame).listen(interaction.onIframeError);
     }
     void onError(String errorMessage) {
+      interaction.consolePrintLine(errorMessage);
       console
-          ..appendText(errorMessage)
-          ..appendText(' ')
           ..append(buildButton('Try in iframe', (_) => retryInIframe()))
           ..appendText('\n');
     }
     interaction.aboutToRun();
     if (usesDartHtml && !alwaysRunInWorker) {
       retryInIframe();
     } else {
       runInWorker(url, onError);
     }
   }
@@ skipping 29 matching lines @@
     if (seenMessages.add('$begin:$end: [$kind] $message')) {
       // Guard against duplicated messages.
       addDiagnostic(kind, message, begin, end);
     }
   }
 
   onCrash(data) {
     interaction.onCompilerCrash(data);
   }
 }