Virtual destructors should have virtual keyword.

chrome/browser/plugin_data_remover_helper.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_PLUGIN_DATA_REMOVER_HELPER_H_
 #define CHROME_BROWSER_PLUGIN_DATA_REMOVER_HELPER_H_
 #pragma once
 
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/prefs/pref_member.h"
 #include "content/common/notification_observer.h"
 #include "content/common/notification_registrar.h"
 
 class Profile;
 
 // Helper class modeled after BooleanPrefMember to (asynchronously) update
 // the preference specifying whether clearing plug-in data is supported
 // by an installed plug-in.
 // It should only be used from the UI thread. The client has to make sure that
 // the passed PrefService outlives this object.
 class PluginDataRemoverHelper : public NotificationObserver {
  public:
   PluginDataRemoverHelper();
-  ~PluginDataRemoverHelper();
+  virtual ~PluginDataRemoverHelper();
 
   // Binds this object to the |pref_name| preference in |prefs|, notifying
   // |observer| if the value changes.
   // This fires off a request to the NPAPI::PluginList (via PluginDataRemover)
   // on the FILE thread to get the list of installed plug-ins.
   void Init(const char* pref_name,
             PrefService* prefs,
             NotificationObserver* observer);
 
   bool GetValue() const { return pref_.GetValue(); }
 
   // NotificationObserver methods:
   virtual void Observe(NotificationType type,
                        const NotificationSource& source,
                        const NotificationDetails& details);
 
  private:
   class Internal;
 
   BooleanPrefMember pref_;
   NotificationRegistrar registrar_;
   scoped_refptr<Internal> internal_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginDataRemoverHelper);
 };
 
 #endif  // CHROME_BROWSER_PLUGIN_DATA_REMOVER_HELPER_H_