Clean up the test srapper code so that it does not use reportTestError, and made that private.

lib/unittest/dom_config.dart

 // 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.
 
 /** Configuration for running tests in a browser using dart:dom_deprecated. */
 #library('dom_config');
 
 #import('dart:dom_deprecated');
 #import('unittest.dart');
 
 #source('html_print.dart');
 
 class DomConfiguration extends Configuration {
   /** Whether this is run within dartium layout tests. */
   final bool _isLayoutTest;
 
   DomConfiguration(this._isLayoutTest);
 
   // TODO(rnystrom): Get rid of this if we get canonical closures for methods.
   EventListener _onErrorClosure;
 
   void onInit() {
-    _onErrorClosure = (e) {
-      // TODO(vsm): figure out how to expose the stack trace here
-      // Currently e.message works in dartium, but not in dartc.
-      reportTestError('(DOM callback has errors) Caught $e', '');
-    };
+    _onErrorClosure =
+        (e) => handleExternalError(e, '(DOM callback has errors)');
   }
 
   void onStart() {
     window.postMessage('unittest-suite-wait-for-done', '*');
     // Listen for uncaught errors.
     window.addEventListener('error', _onErrorClosure, true);
   }
 
   void onTestResult(TestCase testCase) {}
 
   void onDone(int passed, int failed, int errors, List<TestCase> results,
       String uncaughtError) {
     window.removeEventListener('error', _onErrorClosure);
     _showResultsInPage(passed, failed, errors, results, _isLayoutTest,
         uncaughtError);
     window.postMessage('unittest-suite-done', '*');
   }
 }
 
 void useDomConfiguration([bool isLayoutTest = false]) {
   configure(new DomConfiguration(isLayoutTest));
 }