chrome: Cleanup class/struct forward declarations

chrome/browser/media_galleries/media_file_system_context.h

 // Copyright (c) 2012 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_MEDIA_GALLERIES_MEDIA_FILE_SYSTEM_CONTEXT_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FILE_SYSTEM_CONTEXT_H_
 
 // Manages isolated filesystem namespaces for media file systems.
 
 #include <string>
 
 namespace base {
 class FilePath;
 }
 
-class MediaFileSystemRegistry;
-
 class MediaFileSystemContext {
  public:
   virtual ~MediaFileSystemContext() {}
 
   // Register a new media file system for |path| as |fs_name|.
   virtual bool RegisterFileSystem(const std::string& device_id,
                                   const std::string& fs_name,
                                   const base::FilePath& path) = 0;
 
   // Revoke the passed |fs_name|.
   virtual void RevokeFileSystem(const std::string& fs_name) = 0;
 
   // Return the mount point root for the given |fs_name|. Returns an empty path
   // if |fs_name| is not valid.
   virtual base::FilePath GetRegisteredPath(
       const std::string& fs_name) const = 0;
 };
 
 #endif  // CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FILE_SYSTEM_CONTEXT_H_