Add PrerenderLocalPredictor, which will eventually perform

chrome/browser/history/history.cc

Index: chrome/browser/history/history.cc
===================================================================
--- chrome/browser/history/history.cc	(revision 131579)
+++ chrome/browser/history/history.cc	(working copy)
@@ -892,3 +892,16 @@
   ScheduleAndForget(PRIORITY_NORMAL,
                     &HistoryBackend::MigrateThumbnailsDatabase);
 }
+
+void HistoryService::AddVisitDatabaseObserver(
+    history::VisitDatabaseObserver* observer) {
+  LoadBackendIfNecessary();
+  history_backend_->AddVisitDatabaseObserver(observer);
+}
+
+void HistoryService::RemoveVisitDatabaseObserver(
+    history::VisitDatabaseObserver* observer) {
+  // If the history backend is no longer present, nothing to do here.
+  if (history_backend_)
+    history_backend_->RemoveVisitDatabaseObserver(observer);
+}