Virtual destructors should have virtual keyword.

chrome/browser/history/history.h

 // Copyright (c) 2011 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_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_H_
 #pragma once
 
 #include <set>
 #include <vector>
@@ skipping 559 matching lines @@
 
   // Called by TopSites after the thumbnails were read and it is safe
   // to delete the thumbnails DB.
   void OnTopSitesReady();
 
   // Returns true if this looks like the type of URL we want to add to the
   // history. We filter out some URLs such as JavaScript.
   static bool CanAddURL(const GURL& url);
 
  protected:
-  ~HistoryService();
+  virtual ~HistoryService();
 
   // These are not currently used, hopefully we can do something in the future
   // to ensure that the most important things happen first.
   enum SchedulePriority {
     PRIORITY_UI,      // The highest priority (must respond to UI events).
     PRIORITY_NORMAL,  // Normal stuff like adding a page.
     PRIORITY_LOW,     // Low priority things like indexing or expiration.
   };
 
  private:
@@ skipping 276 matching lines @@
   BookmarkService* bookmark_service_;
   bool no_db_;
 
   // True if needs top site migration.
   bool needs_top_sites_migration_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryService);
 };
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_H_