Tame the proliferation of UserContext constructors

chrome/browser/chromeos/login/login_manager_test.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_CHROMEOS_LOGIN_LOGIN_MANAGER_TEST_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_LOGIN_MANAGER_TEST_H_
 
+#include <string>
+
 #include "chrome/browser/chromeos/login/mock_login_utils.h"
 #include "chrome/browser/chromeos/login/test/js_checker.h"
 #include "chrome/test/base/in_process_browser_test.h"
 
 namespace content {
 class WebContents;
 }  // namespace content
 
 namespace chromeos {
 
@@ skipping 57 matching lines @@
   bool should_launch_browser_;
   content::WebContents* web_contents_;
   test::JSChecker js_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(LoginManagerTest);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_LOGIN_MANAGER_TEST_H_