chrome: Cleanup class/struct forward declarations

chrome/browser/sync_file_system/drive_backend/sync_worker_interface.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_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_WORKER_INTERFACE_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_WORKER_INTERFACE_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "chrome/browser/sync_file_system/remote_file_sync_service.h"
 #include "chrome/browser/sync_file_system/sync_action.h"
 #include "chrome/browser/sync_file_system/sync_callbacks.h"
 #include "chrome/browser/sync_file_system/sync_direction.h"
 #include "net/base/network_change_notifier.h"
 
 class GURL;
 
 namespace base {
 class FilePath;
 class ListValue;
 }
 
-namespace drive {
-class DriveServiceInterface;
-class DriveUploaderInterface;
-}
-
 namespace storage {
 class FileSystemURL;
 }
 
 namespace sync_file_system {
 
 class FileChange;
 class SyncFileMetadata;
 
 namespace drive_backend {
 
-class MetadataDatabase;
 class RemoteChangeProcessorOnWorker;
 class SyncEngineContext;
-class SyncTaskManager;
 
 class SyncWorkerInterface {
  public:
   class Observer {
    public:
     virtual void OnPendingFileListUpdated(int item_count) = 0;
     virtual void OnFileStatusChanged(const storage::FileSystemURL& url,
                                      SyncFileType file_type,
                                      SyncFileStatus file_status,
                                      SyncAction sync_action,
@@ skipping 52 matching lines @@
  private:
   friend class SyncEngineTest;
 
   DISALLOW_COPY_AND_ASSIGN(SyncWorkerInterface);
 };
 
 }  // namespace drive_backend
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_WORKER_INTERFACE_H_