chrome: Cleanup class/struct forward declarations

chrome/browser/chromeos/login/auth/mount_manager.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_CHROMEOS_LOGIN_AUTH_MOUNT_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_AUTH_MOUNT_MANAGER_H_
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
 
-class PrefRegistrySimple;
-
 namespace chromeos {
 
 // Keeps track of mount points for different users.
 class MountManager {
  public:
   // Returns a shared instance of a MountManager. Not thread-safe,
   // should only be called from the main UI thread.
   static MountManager* Get();
 
   static base::FilePath GetHomeDir(std::string& user_hash);
@@ skipping 15 matching lines @@
   UserToPathMap additional_mounts_;
 
   static MountManager* instance_;
 
   DISALLOW_COPY_AND_ASSIGN(MountManager);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_AUTH_MOUNT_MANAGER_H_