[Thumbnails DB] Allow setting last_requested time when accessing 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 488 matching lines @@
   FaviconBitmapIDSize();
   ~FaviconBitmapIDSize();
 
   // The unique id of the favicon bitmap.
   FaviconBitmapID bitmap_id = 0;
 
   // The pixel dimensions of the associated bitmap.
   gfx::Size pixel_size;
 };
 
+enum FaviconBitmapType {
+  // The bitmap gets downloaded while visiting its page. Their life-time is
+  // bound to the life-time of the corresponding visit in history.
+  //  - These bitmaps are re-downloaded when visiting the page again and the
+  //  last_updated timestamp is old enough.
+  ON_VISIT,
+
+  // The bitmap gets downloaded because it is demanded by some Chrome UI (while
+  // 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 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_