RefCounted types should not have public destructors, delegate cleanup

chrome/browser/content_settings/content_settings_observer.h

 // Copyright (c) 2012 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_CONTENT_SETTINGS_CONTENT_SETTINGS_OBSERVER_H_
 #define CHROME_BROWSER_CONTENT_SETTINGS_CONTENT_SETTINGS_OBSERVER_H_
 
 #include <string>
 
 #include "chrome/common/content_settings_pattern.h"
 #include "chrome/common/content_settings_types.h"
 
 namespace content_settings {
 
 class Observer {
  public:
   virtual void OnContentSettingChanged(
       const ContentSettingsPattern& primary_pattern,
       const ContentSettingsPattern& secondary_pattern,
       ContentSettingsType content_type,
       std::string resource_identifier) = 0;
+
+ protected:
+  virtual ~Observer() {}
 };
 
 }  // namespace content_settings
 
 #endif  // CHROME_BROWSER_CONTENT_SETTINGS_CONTENT_SETTINGS_OBSERVER_H_