components: Cleanup class/struct fwd declarations

chrome/browser/history/android/bookmark_model_sql_handler.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_HISTORY_ANDROID_BOOKMARK_MODEL_SQL_HANDLER_H_
 #define CHROME_BROWSER_HISTORY_ANDROID_BOOKMARK_MODEL_SQL_HANDLER_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "components/history/core/browser/android/sql_handler.h"
 
 class Profile;
 
 namespace bookmarks {
 class BookmarkModel;
 }
 
 namespace history {
 
 class HistoryDatabase;
+class URLDatabase;
 
 // The SQL handler for bookmarking_mapping table.
 class BookmarkModelSQLHandler : public SQLHandler {
  public:
   explicit BookmarkModelSQLHandler(URLDatabase* url_database);
 
   ~BookmarkModelSQLHandler() override;
 
   // SQLHandler overrides:
   bool Update(const HistoryAndBookmarkRow& row,
@@ skipping 42 matching lines @@
   };
 
   URLDatabase* url_database_;
 
   DISALLOW_COPY_AND_ASSIGN(BookmarkModelSQLHandler);
 };
 
 }  // namespace history.
 
 #endif  // CHROME_BROWSER_HISTORY_ANDROID_BOOKMARK_MODEL_SQL_HANDLER_H_