Make it possible to build without enable_supervised_users.

chrome/browser/component_updater/supervised_user_whitelist_installer.h

 // Copyright 2014 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_COMPONENT_UPDATER_SUPERVISED_USER_WHITELIST_INSTALLER_H_
 #define CHROME_BROWSER_COMPONENT_UPDATER_SUPERVISED_USER_WHITELIST_INSTALLER_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/strings/string16.h"
+#include "chrome/browser/supervised_user/supervised_users.h"
 
 namespace base {
 class FilePath;
 }
 
 class PrefRegistrySimple;
 class PrefService;
 class ProfileAttributesStorage;
 
 namespace component_updater {
@@ skipping 57 matching lines @@
   // called from the implementation subclass, and declared here so that the
   // OnDemandUpdater can friend this class and the implementation subclass can
   // live in an anonymous namespace.
   static void TriggerComponentUpdate(OnDemandUpdater* updater,
                                      const std::string& crx_id);
 };
 
 }  // namespace component_updater
 
 #endif  // CHROME_BROWSER_COMPONENT_UPDATER_SUPERVISED_USER_WHITELIST_INSTALLER_H_