Add PrerenderLocalPredictor, which will eventually perform

chrome/browser/history/history_backend.h

Index: chrome/browser/history/history_backend.h
===================================================================
--- chrome/browser/history/history_backend.h	(revision 131579)
+++ chrome/browser/history/history_backend.h	(working copy)
@@ -378,6 +378,11 @@
   // code to avoid syncing visits that would immediately be expired).
   virtual bool IsExpiredVisitTime(const base::Time& time);
 
+  // Adds or removes observers for the VisitDatabase.  Should be run in the
+  // thread in which the observer would like to be notified.
+  void AddVisitDatabaseObserver(VisitDatabaseObserver* observer);
+  void RemoveVisitDatabaseObserver(VisitDatabaseObserver* observer);
+
  protected:
   virtual ~HistoryBackend();