Eliminate some of the flakiness in testing:

pkg/unittest/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.
  */
 
 if (navigator.webkitStartDart) {
@@ skipping 53 matching lines @@
     showErrorAndExit(window.compilationError);
   }
 }
 
 window.addEventListener("DOMContentLoaded", onLoad, false);
 
 // If nobody intercepts the error, finish the test.
 window.addEventListener("error", function(e) {
   // needed for dartium compilation errors.
   showErrorAndExit(e && e.message);
+  window.postMessage('unittest-suite-external-error', '*');
 }, false);
 
 document.addEventListener('readystatechange', function () {
   if (document.readyState != "loaded") return;
   // If 'startedDartTest' is not set, that means that the test did not have
   // a chance to load. This will happen when a load error occurs in the VM.
   // Give the machine time to start up.
   setTimeout(function() {
     // A window.postMessage might have been enqueued after this timeout.
     // Just sleep another time to give the browser the time to process the
@@ skipping 27 matching lines @@
 function dartMainRunner(main) {
   window.postMessage('dart-calling-main', '*');
   try {
     main();
   } catch (e) {
     window.postMessage('unittest-suite-fail', '*');
     return;
   }
   window.postMessage('dart-main-done', '*');
 }