content: Cleanup class/struct forward declarations

content/browser/notifications/notification_database.h

 // Copyright 2015 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 CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_DATABASE_H_
 #define CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_DATABASE_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <set>
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/sequence_checker.h"
 #include "content/common/content_export.h"
 
 class GURL;
 
 namespace leveldb {
 class DB;
 class Env;
 class FilterPolicy;
-class WriteBatch;
 }
 
 namespace content {
 
 struct NotificationDatabaseData;
 
 // Implementation of the persistent notification database.
 //
 // The database is built on top of a LevelDB database, either in memory or on
 // the filesystem depending on the path passed to the constructor. When writing
@@ skipping 171 matching lines @@
   State state_ = STATE_UNINITIALIZED;
 
   base::SequenceChecker sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NotificationDatabase);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_DATABASE_H_