Make it possible to build without enable_supervised_users.

chrome/browser/supervised_user/supervised_user_creation_policy_handler.h

 // Copyright 2016 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_SUPERVISED_USER_SUPERVISED_USER_CREATION_POLICY_HANDLER_H_
 #define CHROME_BROWSER_SUPERVISED_USER_SUPERVISED_USER_CREATION_POLICY_HANDLER_H_
 
 #include "base/macros.h"
+#include "chrome/browser/supervised_user/supervised_users.h"
 #include "components/policy/core/browser/configuration_policy_handler.h"
 
 class PrefValueMap;
 
 namespace policy {
 
 class PolicyMap;
 
 class SupervisedUserCreationPolicyHandler : public TypeCheckingPolicyHandler {
  public:
   SupervisedUserCreationPolicyHandler();
   ~SupervisedUserCreationPolicyHandler() override;
 
   void ApplyPolicySettings(const PolicyMap& policies,
                            PrefValueMap* prefs) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SupervisedUserCreationPolicyHandler);
 };
 
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_SUPERVISED_USER_SUPERVISED_USER_CREATION_POLICY_HANDLER_H_