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

lib/unittest/html_enhanced_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.
 
 /**
  * A simple unit test library for running tests in a browser.
  *
  * Provides enhanced HTML output with collapsible group headers
  * and other at-a-glance information about the test results.
  */
@@ skipping 17 matching lines @@
 
     var cssElement = document.head.query('#${_CSSID}');
     if (cssElement == null){
       document.head.elements.add(new Element.html(
           '<style id="${_CSSID}"></style>'));
       cssElement = document.head.query('#${_CSSID}');
     }
 
     cssElement.innerHTML = _htmlTestCSS;
 
-    _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.on.error.add(_onErrorClosure);
   }
 
   void onTestResult(TestCase testCase) {}
 
@@ skipping 311 matching lines @@
   .unittest-row-description
   {
   }
 
   ''';
 }
 
 void useHtmlEnhancedConfiguration([bool isLayoutTest = false]) {
   configure(new HtmlEnhancedConfiguration(isLayoutTest));
 }