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

components/history/core/browser/history_types.h

 // Copyright 2014 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_TYPES_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_TYPES_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 506 matching lines @@
   // not visiting its page). For this reason, their life-time cannot be bound to
   // the life-time of the corresponding visit in history.
   // - These bitmaps are evicted from the database based on the last time they
   //   were requested.
   // - Furthermore, on-demand bitmaps are immediately marked as expired. Hence,
   //   they are always replaced by ON_VISIT favicons whenever their page gets
   //   visited.
   ON_DEMAND
 };
 
+// Defines all associated mappings of a given favicon.
+struct IconMappingsForExpiry {
+  IconMappingsForExpiry();
+  IconMappingsForExpiry(const IconMappingsForExpiry& other);
+  ~IconMappingsForExpiry();
+
+  // URL of a given favicon.
+  GURL icon_url;
+  // URLs of all pages mapped to a given favicon
+  std::vector<GURL> page_urls;
+};
+
 // Defines a favicon bitmap stored in the history backend.
 struct FaviconBitmap {
   FaviconBitmap();
   FaviconBitmap(const FaviconBitmap& other);
   ~FaviconBitmap();
 
   // The unique id of the bitmap.
   FaviconBitmapID bitmap_id = 0;
 
   // The id of the favicon to which the bitmap belongs to.
@@ skipping 22 matching lines @@
   void SetTimeRangeForOneDay(base::Time time);
 
   std::set<GURL> urls;
   base::Time begin_time;
   base::Time end_time;
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_TYPES_H_