Fix a syntax error in webdriver.

pkg/webdriver/lib/webdriver.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.
 
 library webdriver;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:json' as json;
 import 'dart:uri';
@@ skipping 199 matching lines @@
 
   WebDriverBase([
       this._host = 'localhost',
       this._port = 4444,
       this._path = '/wd/hub']) {
     _url = 'http://$_host:$_port$_path';
   }
 
   void _failRequest(Completer completer, error, [stackTrace]) {
     if (completer != null) {
-      var trace = stackTrace != null ? stackTrace, getAttachedStackTrace(error);
+      var trace = stackTrace != null ? stackTrace : getAttachedStackTrace(error);
       completer.completeError(new WebDriverError(-1, error), trace);
     }
   }
 
   /**
    * Execute a request to the WebDriver server. [http_method] should be
    * one of 'GET', 'POST', or 'DELETE'. [command] is the text to append
    * to the base URL path to get the full URL. [params] are the additional
    * parameters. If a [List] or [Map] they will be posted as JSON parameters.
    * If a number or string, "/params" is appended to the URL.
@@ skipping 1211 matching lines @@
    *
    * 'timestamp' (int) - The timestamp of the entry.
    * 'level' (String) - The log level of the entry, for example, "INFO".
    * 'message' (String) - The log message.
    *
    * This works with Firefox but Chrome returns a 500 response due to a 
    * bad cast.
    */
   Future<List<Map>> getLogs(String type) => _post('log', { 'type': type });
 }