[Thumbnails DB] Allow setting last_requested time when accessing favicons.
This CL deals with favicons that are added without the user visiting the corresponding
page. The CL introduces the notion of "on-demand" favicons for them:
1) The CL reuses (and renames) an existing function in FaviconService for storing
such on-demand favicons and pushes this concept further to ThumbnailDatabase.
2) The CL adds a new function to touch (i.e. update last_requested time-stamp) for
"on-deman" favicons.
The functionality to clear unused on-demand favicons is left for a further CL
(https://codereview.chromium.org/2903573002/). Similarly, calling
TouchOnDemandFavicon from LargeIconService is also left for a later CL.
BUG=709471
Review-Url: https://codereview.chromium.org/2856873002
Cr-Commit-Position: refs/heads/master@{#481232}
16 files changed
