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

components/history/core/browser/expire_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_EXPIRE_HISTORY_BACKEND_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_
 
 #include <memory>
 #include <queue>
 #include <set>
@@ skipping 161 matching lines @@
   //
   // The visits in the given vector should have already been deleted from the
   // database, and the list of affected URLs already be filled into
   // |depenencies->affected_urls|.
   //
   // Starred URLs will not be deleted. The information in the dependencies that
   // DeleteOneURL fills in will be updated, and this function will also delete
   // any now-unused favicons.
   void ExpireURLsForVisits(const VisitVector& visits, DeleteEffects* effects);
 
+  // Clears all old on-demand favicons from thumbnail database.
+  void ClearOldOnDemandFavicons();
+
   // Deletes the favicons listed in |effects->affected_favicons| if they are
   // unsued. Fails silently (we don't care about favicons so much, so don't want
   // to stop everything if it fails). Fills |expired_favicons| with the set of
   // favicon urls that no longer have associated visits and were therefore
   // expired.
   void DeleteFaviconsIfPossible(DeleteEffects* effects);
 
   // Enum representing what type of action resulted in the history DB deletion.
   enum DeletionType {
     // User initiated the deletion from the History UI.
@@ skipping 71 matching lines @@
   // Used to generate runnable methods to do timers on this class. They will be
   // automatically canceled when this class is deleted.
   base::WeakPtrFactory<ExpireHistoryBackend> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExpireHistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_