Virtual destructors should have virtual keyword.

content/browser/host_zoom_map.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.
 
 // Maps hostnames to custom zoom levels.  Written on the UI thread and read on
 // any thread.  One instance per profile.
 
 #ifndef CONTENT_BROWSER_HOST_ZOOM_MAP_H_
 #define CONTENT_BROWSER_HOST_ZOOM_MAP_H_
 #pragma once
@@ skipping 59 matching lines @@
 
   double default_zoom_level() const { return default_zoom_level_; }
   void set_default_zoom_level(double level) { default_zoom_level_ = level; }
 
  private:
   friend struct BrowserThread::DeleteOnThread<BrowserThread::UI>;
   friend class DeleteTask<HostZoomMap>;
 
   typedef std::map<std::string, double> HostZoomLevels;
 
-  ~HostZoomMap();
+  virtual ~HostZoomMap();
 
   // Copy of the pref data, so that we can read it on the IO thread.
   HostZoomLevels host_zoom_levels_;
   double default_zoom_level_;
 
   struct TemporaryZoomLevel {
     int render_process_id;
     int render_view_id;
     double zoom_level;
   };
 
   // Don't expect more than a couple of tabs that are using a temporary zoom
   // level, so vector is fine for now.
   std::vector<TemporaryZoomLevel> temporary_zoom_levels_;
 
   // Used around accesses to |host_zoom_levels_|, |default_zoom_level_| and
   // |temporary_zoom_levels_| to guarantee thread safety.
   mutable base::Lock lock_;
 
   NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(HostZoomMap);
 };
 
 #endif  // CONTENT_BROWSER_HOST_ZOOM_MAP_H_