Don't dispatch events when XHR is set to sync mode

LayoutTests/http/tests/xmlhttprequest/connection-error-sync.html

Index: LayoutTests/http/tests/xmlhttprequest/connection-error-sync.html
diff --git a/LayoutTests/http/tests/xmlhttprequest/connection-error-sync.html b/LayoutTests/http/tests/xmlhttprequest/connection-error-sync.html
index 7600aa129d4dffeead163e4c3028691fb77e39fb..fad290524dc21258637e70b4b17227be0407ba67 100644
--- a/LayoutTests/http/tests/xmlhttprequest/connection-error-sync.html
+++ b/LayoutTests/http/tests/xmlhttprequest/connection-error-sync.html
@@ -19,6 +19,14 @@
         }
         
         req.open('GET', 'resources/infinite-loop.php', false);
+        req.onreadystatechange = function()
+        {
+            document.write('onreadystatechange is invoked unexpectedly<br>');
+        }
+        req.onerror = function()
+        {
+            document.write('onerror is invoked unexpectedly<br>');
+        }
         req.send(null);
 
         document.write("Status: " + req.status);