Bug 853188 - Use the url and line number passed to window.onerror, r=mdas

testing/marionette/marionette-listener.js

@@ -519,7 +519,7 @@ function executeWithCallback(msg, useFinish) {
 
   originalOnError = curWindow.onerror;
   curWindow.onerror = function errHandler(errMsg, url, line) {
-    sandbox.asyncComplete(errMsg, 17, null, asyncTestCommandId);
+    sandbox.asyncComplete(errMsg, 17, "@" + url + ", line " + line, asyncTestCommandId);
     curWindow.onerror = originalOnError;
   };