This interface can be used to add a download to history.  There is a separate
 interface specifically for downloads in case embedders choose to track
 downloads differently from other types of history.
[scriptable, uuid(202533cd-a8f1-4ee4-8d20-3a6a0d2c6c51)]
interface nsIDownloadHistory : nsISupports


 Adds a download to history.  This will also notify observers that the
 URI aSource is visited with the topic NS_LINK_VISITED_EVENT_TOPIC if
 aSource has not yet been visited.

 @param aSource
        The source of the download we are adding to history.  This cannot be
 @param aReferrer
        [optional] The referrer of source URI.
 @param aStartTime
        [optional] The time the download was started.  If the start time
        is not given, the current time is used.
         In a situation where a history implementation is not available,
         where 'history implementation' refers to something like
         nsIGlobalHistory and friends.
void addDownload(in nsIURI aSource, [optional] in nsIURI aReferrer, [optional] in PRTime aStartTime)