[Thumbnails DB] Allow setting last_requested time when accessing favicons.

components/history/core/browser/history_service.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_SERVICE_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_SERVICE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 738 matching lines @@
                    favicon_base::IconType icon_type,
                    const GURL& icon_url,
                    const std::vector<SkBitmap>& bitmaps);
 
   // Same as SetFavicons with three differences:
   // 1) It will be a no-op if there is an existing cached favicon for *any* type
   //    for |page_url|.
   // 2) If |icon_url| is known to the database, |bitmaps| will be ignored (i.e.
   //    the icon won't be overwritten) but the mappings from |page_url| to
   //    |icon_url| will be stored (conditioned to point 1 above).
-  // 3) If |icon_url| is stored, it will be marked as expired.
+  // 3) If |icon_url| is stored, it will be marked as "on-demand".
+  //
+  // On-demand favicons are those that are fetched without visiting their 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
+  //   get requested. The last requested time is initially set to Now() and is
+  //   further updated by calling TouchOnDemandFavicon().
+  // - Furthermore, on-demand bitmaps are immediately marked as expired. Hence,
+  //   they are always replaced by standard favicons whenever their page gets
+  //   visited.
   // The callback will receive whether the write actually happened.
-  void SetLastResortFavicons(const GURL& page_url,
-                             favicon_base::IconType icon_type,
-                             const GURL& icon_url,
-                             const std::vector<SkBitmap>& bitmaps,
-                             base::Callback<void(bool)> callback);
+  void SetOnDemandFavicons(const GURL& page_url,
+                           favicon_base::IconType icon_type,
+                           const GURL& icon_url,
+                           const std::vector<SkBitmap>& bitmaps,
+                           base::Callback<void(bool)> callback);
 
   // Used by the FaviconService to mark the favicon for the page as being out
   // of date.
   void SetFaviconsOutOfDateForPage(const GURL& page_url);
 
+  // Mark that the on-demand favicon at |icon_url| was requested now. This
+  // postpones the automatic eviction of the favicon from the database. Not all
+  // calls end up in a write into the DB:
+  // - it is no-op if the bitmaps are not stored using SetOnDemandFavicons();
+  // - the updates of the last requested time have limited frequency for each

[pkotwicz, 2017/06/07 17:40:52]

Nit: Add quotes around "last requested time"

[jkrcal, 2017/06/09 16:38:37]

Done.

+  //   particular favicon (e.g. once per week). This limits the overhead of
+  //   cache management for on-demand favicons.
+  void TouchOnDemandFavicon(const GURL& icon_url);
+
   // Used by the FaviconService for importing many favicons for many pages at
   // once. The pages must exist, any favicon sets for unknown pages will be
   // discarded. Existing favicons will not be overwritten.
   void SetImportedFavicons(
       const favicon_base::FaviconUsageDataList& favicon_usage);
 
   // Sets the in-memory URL database. This is called by the backend once the
   // database is loaded to make it available.
   void SetInMemoryBackend(std::unique_ptr<InMemoryHistoryBackend> mem_backend);
 
@@ skipping 58 matching lines @@
 
   // All vended weak pointers are invalidated in Cleanup().
   base::WeakPtrFactory<HistoryService> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryService);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_SERVICE_H_