The HistoryBackend consists of a number of components:  

HistoryDatabase (stores past 3 months of history)      

ArchivedDatabase (stores history older than 3 months)      

      (this does not store visit segments as they expire after 3 months)

TextDatabaseManager (manages multiple text database for different times)      

ExpireHistoryBackend (manages moving things from HistoryDatabase to the ArchivedDatabase and deleting)

 

Static ConstantValue 
Segment Data Retention90 daysHow long Chrome keeps segment data for in days.  Currently 3 months.
Commit Interval Seconds10 secondsHow long Chrome waits to do a commit, so that things are batched together.
Favicon Refetch Days7 daysThe amount of time before Chrome re-fetches the favicon.
Archive Days Threshold90 daysThe number of days old a history entry can be before it is considered "old" and is archived.