[Thumbnails DB] Add functionality to clear unused on-demand favicons.

components/history/core/browser/thumbnail_database.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_THUMBNAIL_DATABASE_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_THUMBNAIL_DATABASE_H_
 
 #include <vector>
 
 #include "base/gtest_prod_util.h"
@@ skipping 44 matching lines @@
   void RollbackTransaction();
 
   // Vacuums the database. This will cause sqlite to defragment and collect
   // unused space in the file. It can be VERY SLOW.
   void Vacuum();
 
   // Try to trim the cache memory used by the database.  If |aggressively| is
   // true try to trim all unused cache, otherwise trim by half.
   void TrimMemory(bool aggressively);
 
+  // Delete all on-demand favicon bitmaps that have not been requested long
+  // (i.e. not after |expiration_threshold|). Do not delete bitmaps for URLs
+  // that are bookmarked in |bookmark_model|. Furthermore, delete all favicons
+  // with no corresponding bitmap and all mappings with no corresponding
+  // favicon.
+  void ClearOldOnDemandFavicons(base::Time expiration_threshold);
+
   // Favicon Bitmaps -----------------------------------------------------------
 
   // Returns true if there are favicon bitmaps for |icon_id|. If
   // |bitmap_id_sizes| is non NULL, sets it to a list of the favicon bitmap ids
   // and their associated pixel sizes for the favicon with |icon_id|.
   // The list contains results for the bitmaps which are cached in the
   // favicon_bitmaps table. The pixel sizes are a subset of the sizes in the
   // 'sizes' field of the favicons table for |icon_id|.
   bool GetFaviconBitmapIDSizes(
       favicon_base::FaviconID icon_id,
@@ skipping 210 matching lines @@
 
   sql::Connection db_;
   sql::MetaTable meta_table_;
 
   HistoryBackendClient* backend_client_;
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_THUMBNAIL_DATABASE_H_