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

components/favicon/core/favicon_service.h

 // Copyright (c) 2017 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_FAVICON_CORE_FAVICON_SERVICE_H_
 #define COMPONENTS_FAVICON_CORE_FAVICON_SERVICE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 121 matching lines @@
   // multiple favicon bitmaps for |favicon_id|, the largest favicon bitmap is
   // returned.
   virtual base::CancelableTaskTracker::TaskId GetLargestRawFaviconForID(
       favicon_base::FaviconID favicon_id,
       const favicon_base::FaviconRawBitmapCallback& callback,
       base::CancelableTaskTracker* tracker) = 0;
 
   // Marks all types of favicon for the page as being out of date.
   virtual void SetFaviconOutOfDateForPage(const GURL& page_url) = 0;
 
+  // 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
+  //   particular favicon (e.g. once per week). This limits the overhead of
+  //   cache management for on-demand favicons.
+  virtual void TouchOnDemandFavicon(const GURL& icon_url) = 0;
+
   // Allows the importer to set 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.
   virtual void SetImportedFavicons(
       const favicon_base::FaviconUsageDataList& favicon_usage) = 0;
 
   // Set the favicon for |page_url| for |icon_type| in the thumbnail database.
   // Unlike SetFavicons(), this method will not delete preexisting bitmap data
   // which is associated to |page_url| if at all possible. Use this method if
   // the favicon bitmaps for any of ui::GetSupportedScaleFactors() are not
@@ skipping 12 matching lines @@
   // contains image reps for all of ui::GetSupportedScaleFactors(). Use
   // MergeFavicon() if it does not.
   // TODO(pkotwicz): Save unresized favicon bitmaps to the database.
   // TODO(pkotwicz): Support adding favicons for multiple icon URLs to the
   // thumbnail database.
   virtual void SetFavicons(const GURL& page_url,
                            const GURL& icon_url,
                            favicon_base::IconType icon_type,
                            const gfx::Image& image) = 0;
 
-  // Same as SetFavicons() with three differences:
+  // 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.
-  virtual void SetLastResortFavicons(const GURL& page_url,
-                                     const GURL& icon_url,
-                                     favicon_base::IconType icon_type,
-                                     const gfx::Image& image,
-                                     base::Callback<void(bool)> callback) = 0;
+  virtual void SetOnDemandFavicons(const GURL& page_url,
+                                   const GURL& icon_url,
+                                   favicon_base::IconType icon_type,
+                                   const gfx::Image& image,
+                                   base::Callback<void(bool)> callback) = 0;
 
   // Avoid repeated requests to download missing favicon.
   virtual void UnableToDownloadFavicon(const GURL& icon_url) = 0;
   virtual bool WasUnableToDownloadFavicon(const GURL& icon_url) const = 0;
   virtual void ClearUnableToDownloadFavicons() = 0;
 };
 
 }  // namespace favicon
 
 #endif  // COMPONENTS_FAVICON_CORE_FAVICON_SERVICE_H_