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

components/history/core/browser/thumbnail_database.h

Index: components/history/core/browser/thumbnail_database.h
diff --git a/components/history/core/browser/thumbnail_database.h b/components/history/core/browser/thumbnail_database.h
index ec21369d43830d0025471da7bfc3c42dd1803a0d..06873fe335e5e758b4777bb6580d2363cb384b7d 100644
--- a/components/history/core/browser/thumbnail_database.h
+++ b/components/history/core/browser/thumbnail_database.h
@@ -101,6 +101,23 @@ class ThumbnailDatabase {
       base::Time time,
       const gfx::Size& pixel_size);
 
+  // The same as AddFaviconBitmap(), it also marks the bitmap as "on-demand".
+  //
+  // On-demand bitmaps 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 |time| and is
+  //   further updated by calling KeepOnDemandFavicon().
+  // - Furthermore, on-demand bitmaps are immediately marked as expired. Hence,
+  //   they are always replaced by standard favicons whenever their page gets
+  //   visited.
+  FaviconBitmapID AddOnDemandFaviconBitmap(
+      favicon_base::FaviconID icon_id,
+      const scoped_refptr<base::RefCountedMemory>& icon_data,
+      base::Time time,
+      const gfx::Size& pixel_size);
+
   // Sets the bitmap data and the last updated time for the favicon bitmap at
   // |bitmap_id|.
   // Returns true if successful.
@@ -113,11 +130,6 @@ class ThumbnailDatabase {
   bool SetFaviconBitmapLastUpdateTime(FaviconBitmapID bitmap_id,
                                       base::Time time);
 
-  // Sets the last requested time for the favicon bitmap at |bitmap_id|.
-  // Returns true if successful.
-  bool SetFaviconBitmapLastRequestedTime(FaviconBitmapID bitmap_id,
-                                         base::Time time);
-
   // Deletes the favicon bitmap with |bitmap_id|.
   // Returns true if successful.
   bool DeleteFaviconBitmap(FaviconBitmapID bitmap_id);
@@ -128,6 +140,16 @@ class ThumbnailDatabase {
   // of the bitmaps for |icon_id| to be out of date.
   bool SetFaviconOutOfDate(favicon_base::FaviconID icon_id);
 
+  // Mark all on-demand bitmaps at |icon_url| as requested at |time|. This
+  // postpones their automatic eviction 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 SetOnDemandFaviconBitmap;
+  // - the updates of the last requested time have limited frequency for each
+  //   particular bitmap (e.g. once per week). This limits the overhead of
+  //   cache management for on-demand favicons.
+  // Returns true if successful.
+  bool TouchOnDemandFavicon(const GURL& icon_url, base::Time time);
+
   // Returns the id of the entry in the favicon database with the specified url
   // and icon type.
   // Returns 0 if no entry exists for the specified url.