Stop history search going on beyond the start of history....

chrome/browser/history/history_backend.h

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H__
 #define CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H__
 
 #include <utility>
 
 #include "base/gfx/rect.h"
@@ skipping 126 matching lines @@
                 const GURL& url,
                 bool want_visits);
   void QueryHistory(scoped_refptr<QueryHistoryRequest> request,
                     const std::wstring& text_query,
                     const QueryOptions& options);
   void QueryRedirectsFrom(scoped_refptr<QueryRedirectsRequest> request,
                           const GURL& url);
 
   void GetVisitCountToHost(scoped_refptr<GetVisitCountToHostRequest> request,
                            const GURL& url);
-
   // Computes the most recent URL(s) that the given canonical URL has
   // redirected to and returns true on success. There may be more than one
   // redirect in a row, so this function will fill the given array with the
   // entire chain. If there are no redirects for the most recent visit of the
   // URL, or the URL is not in history, returns false.
   //
   // Backend for QueryRedirectsFrom.
   bool GetMostRecentRedirectsFrom(const GURL& url,
                                   HistoryService::RedirectList* redirects);
 
@@ skipping 296 matching lines @@
   // to the database by using the last_recorded_time_ (q.v.). We still can't
   // enforce or guarantee uniqueness, since the user might set his clock back.
   base::Time last_requested_time_;
 
   // Timestamp of the last page addition, as it was recorded in the database.
   // If two or more requests come in at the same time, we increment that time
   // by 1 us between them so it's more likely to be unique in the database.
   // This keeps track of that higher-resolution timestamp.
   base::Time last_recorded_time_;
 
+  // Timestamp of the first entry in our database.
+  base::Time first_recorded_time_;
+
   // When non-NULL, this is the task that should be invoked on
   MessageLoop* backend_destroy_message_loop_;
   Task* backend_destroy_task_;
 
   // Tracks page transition types.
   VisitTracker tracker_;
 
   // A boolean variable to track whether we have already purged obsolete segment
   // data.
   bool segment_queried_;
@@ skipping 12 matching lines @@
   // Publishes the history to all indexers which are registered to receive
   // history data from us. Can be NULL if there are no listeners.
   scoped_ptr<HistoryPublisher> history_publisher_;
 
   DISALLOW_EVIL_CONSTRUCTORS(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_BACKEND_H__