components: Cleanup class/struct fwd declarations

components/history/core/browser/history_backend.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 COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 16 matching lines @@
 #include "build/build_config.h"
 #include "components/favicon_base/favicon_usage_data.h"
 #include "components/history/core/browser/expire_history_backend.h"
 #include "components/history/core/browser/history_backend_notifier.h"
 #include "components/history/core/browser/history_types.h"
 #include "components/history/core/browser/keyword_id.h"
 #include "components/history/core/browser/thumbnail_database.h"
 #include "components/history/core/browser/visit_tracker.h"
 #include "sql/init_status.h"
 
-class HistoryURLProvider;
-struct HistoryURLProviderParams;
 class SkBitmap;
 class TestingProfile;
-struct ThumbnailScore;
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace history {
 class CommitLaterTask;
 struct DownloadRow;
 class HistoryBackendClient;
 class HistoryBackendDBBaseTest;
 class HistoryBackendObserver;
 class HistoryBackendTest;
 class HistoryDatabase;
 struct HistoryDatabaseParams;
-struct HistoryDetails;
 class HistoryDBTask;
 class InMemoryHistoryBackend;
 class TypedUrlSyncableService;
 class HistoryBackendHelper;
+class URLDatabase;
 
 // The maximum number of icons URLs per page which can be stored in the
 // thumbnail database.
 static const size_t kMaxFaviconsPerPage = 8;
 
 // The maximum number of bitmaps for a single icon URL which can be stored in
 // the thumbnail database.
 static const size_t kMaxFaviconBitmapsPerIconURL = 8;
 
 // Keeps track of a queued HistoryDBTask. This class lives solely on the
@@ skipping 821 matching lines @@
 
   // List of observers
   base::ObserverList<HistoryBackendObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_