chrome: Cleanup class/struct forward declarations

chrome/browser/sync_file_system/local/canned_syncable_file_system.h

 // Copyright 2013 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_LOCAL_CANNED_SYNCABLE_FILE_SYSTEM_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_LOCAL_CANNED_SYNCABLE_FILE_SYSTEM_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 10 matching lines @@
 #include "storage/browser/blob/blob_data_handle.h"
 #include "storage/browser/fileapi/file_system_operation.h"
 #include "storage/browser/fileapi/file_system_url.h"
 #include "storage/browser/quota/quota_callbacks.h"
 #include "storage/common/fileapi/file_system_types.h"
 #include "storage/common/fileapi/file_system_util.h"
 #include "storage/common/quota/quota_types.h"
 
 namespace base {
 class SingleThreadTaskRunner;
-class Thread;
 }
 
 namespace storage {
 class FileSystemContext;
 class FileSystemOperationRunner;
 class FileSystemURL;
 }
 
 namespace leveldb {
 class Env;
@@ skipping 209 matching lines @@
   bool is_filesystem_opened_;  // Should be accessed only on the IO thread.
 
   scoped_refptr<ObserverList> sync_status_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(CannedSyncableFileSystem);
 };
 
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_LOCAL_CANNED_SYNCABLE_FILE_SYSTEM_H_