Add PrerenderLocalPredictor, which will eventually perform

chrome/browser/history/visit_database.h

Index: chrome/browser/history/visit_database.h
===================================================================
--- chrome/browser/history/visit_database.h	(revision 131579)
+++ chrome/browser/history/visit_database.h	(working copy)
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_HISTORY_VISIT_DATABASE_H_
 #pragma once
 
+#include "base/observer_list_threadsafe.h"
 #include "chrome/browser/history/history_types.h"
 
 namespace sql {
@@ -17,6 +18,20 @@
 
 class VisitFilter;
 
+// Abbreviated information about a visit.
+struct BriefVisitInfo {
+  URLID url_id;
+  base::Time time;
+  content::PageTransition transition;
+};
+
+// An observer of VisitDatabase.
+class VisitDatabaseObserver {

[cbentzel, 2012/04/17 20:28:16]

Should this handle DeleteVisit and UpdateVisit as well?

[tburkard, 2012/04/17 20:51:36]

I'm not concerned about these for now, the majority of operations is adding
visits.  We may add that later.

On 2012/04/17 20:28:16, cbentzel wrote:

+ public:
+  virtual ~VisitDatabaseObserver() {}
+  virtual void OnAddVisit(BriefVisitInfo info) = 0;

[cbentzel, 2012/04/17 20:28:16]

Why doesn't this take a const VisitRow& as an argument?

[tburkard, 2012/04/17 20:51:36]

Either would work.  I figured I'd use BriefVisitInfo since that was the
information I needed, so at the place where I'm using it, everything is
BriefVisitInfo's.

On 2012/04/17 20:28:16, cbentzel wrote:

[cbentzel, 2012/04/17 20:57:51]

Brett should make the call here - and OWNERS requires it :)

+};
+
 // A visit database is one which stores visits for URLs, that is, times and
 // linking information. A visit database must also be a URLDatabase, as this
 // modifies tables used by URLs directly and could be thought of as inheriting
@@ -172,6 +187,17 @@
   void GetVisitsSource(const VisitVector& visits,
                        VisitSourceMap* sources);
 
+  // Adds or removes observers for the VisitDatabase.  Should be run on
+  // the thread in which the observer would like to be notified.
+  void AddVisitDatabaseObserver(VisitDatabaseObserver* observer);
+  void RemoveVisitDatabaseObserver(VisitDatabaseObserver* observer);
+
+  // Obtains BriefVisitInfo for the specified number of most recent visits
+  // from the visit database.
+  void GetBriefVisitInfoOfMostRecentVisits(
+      int max_visits,
+      std::vector<BriefVisitInfo>* result_vector);
+
  protected:
   // Returns the database for the functions in this interface.
   virtual sql::Connection& GetDB() = 0;
@@ -193,6 +219,7 @@
   bool MigrateVisitsWithoutDuration();
 
  private:
+  scoped_refptr<ObserverListThreadSafe<VisitDatabaseObserver> > observers_;
 
   DISALLOW_COPY_AND_ASSIGN(VisitDatabase);
 };