Provide more information about non-unittest failures.

dart/pkg/unittest/lib/test_controller.js

 // 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.
 
 /**
  * Test controller logic - used by unit test harness to embed tests in
  * DumpRenderTree.
  */
 
 // Clear the console before every test run - this is Firebug specific code.
@@ skipping 117 matching lines @@
   document.body.appendChild(pre);
 }
 
 // dart2js will generate code to call this function instead of calling
 // Dart [main] directly. The argument is a closure that invokes main.
 function dartMainRunner(main) {
   window.postMessage('dart-calling-main', '*');
   try {
     main();
   } catch (e) {
+    dartPrint(e);
+    if (e.stack) dartPrint(e.stack);
     window.postMessage('unittest-suite-fail', '*');
     return;
   }
   window.postMessage('dart-main-done', '*');
 }