Bug fix in browser testing: add null check.

tools/testing/dart/browser_controller.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 browser;
 
 import "dart:async";
 import "dart:convert" show UTF8, JSON;
 import "dart:core";
 import "dart:io";
 import "dart:math" show min;
@@ skipping 1787 matching lines @@
               }
             }
             reportMessage(message, isFirstMessage, isStatusUpdate);
           }
         }
       }
 
       function sendStatusUpdate () {
         var dom =
             embedded_iframe.contentWindow.document.documentElement.innerHTML;
-        reportMessage('Status:\\n  Messages received multiple times:\\n    ' +
-                      html_test.double_received_messages +
-                      '\\n  Unexpected messages:\\n    ' +
-                      html_test.unexpected_messages +
-                      '\\n  DOM:\\n    ' + dom, false, true);
+        var message = 'Status:\\n';
+        if (html_test != null) {
+          message +=
+            '  Messages received multiple times:\\n' +
+            '    ' + html_test.double_received_messages + '\\n' +
+            '  Unexpected messages:\\n' +
+            '    ' + html_test.unexpected_messages + '\\n';
+        }
+        message += '  DOM:\\n' +
+                   '    ' + dom;
+        reportMessage(message, false, true);
       }
 
       function sendRepeatingStatusUpdate() {
         sendStatusUpdate();
         setTimeout(sendRepeatingStatusUpdate, STATUS_UPDATE_INTERVAL);
       }
 
       // HTML tests post messages to their own window, handled by this handler.
       // This handler is installed on the child window when it sends the
       // 'detect_errors' event.  Every HTML test must send 'detect_errors' to
@@ skipping 48 matching lines @@
     </div>
     <div id="embedded_iframe_div" class="test box">
       <iframe id="embedded_iframe"></iframe>
     </div>
   </body>
 </html>
 """;
     return driverContent;
   }
 }