[Thumbnails DB] Add functionality to clear unused on-demand 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 697faf3abec0a6d18d3dc8639ae869e732116ad8..8cda81f322049ca7812857da55491e1d80d9d656 100644
--- a/components/history/core/browser/thumbnail_database.h
+++ b/components/history/core/browser/thumbnail_database.h
@@ -66,6 +66,11 @@ class ThumbnailDatabase {
   // true try to trim all unused cache, otherwise trim by half.
   void TrimMemory(bool aggressively);
 
+  // Get all on-demand favicon bitmaps that have not been requested long
+  // (i.e. not after |threshold|).

[pkotwicz, 2017/07/07 00:42:38]

How about: "that have been requested prior to |threshold|."

[jkrcal, 2017/07/07 08:45:16]

Done.

+  std::vector<std::pair<favicon_base::FaviconID, GURL>> GetOldOnDemandFavicons(
+      base::Time threshold);
+
   // Favicon Bitmaps -----------------------------------------------------------
 
   // Returns true if there are favicon bitmaps for |icon_id|. If
@@ -200,6 +205,10 @@ class ThumbnailDatabase {
   // Returns true if the deletion succeeded.
   bool DeleteIconMappings(const GURL& page_url);
 
+  // Deletes the icon mapping entries for the given favicon.
+  // Returns true if the deletion succeeded.
+  bool DeleteIconMappingsForFaviconId(favicon_base::FaviconID id);
+
   // Deletes the icon mapping with |mapping_id|.
   // Returns true if the deletion succeeded.
   bool DeleteIconMapping(IconMappingID mapping_id);