RefCounted types should not have public destructors, delegate cleanup

chrome/browser/extensions/extension_pref_value_map.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_EXTENSIONS_EXTENSION_PREF_VALUE_MAP_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_PREF_VALUE_MAP_H_
 #pragma once
 
 #include <map>
 #include <set>
@@ skipping 33 matching lines @@
 //     1   |   2   |   3   |   4   |   3   |   4
 // A = extension A, B = extension B, E = effective value
 // .reg = regular value
 // .inc = incognito value
 // Extension B has higher precedence than A.
 class ExtensionPrefValueMap : public ProfileKeyedService {
  public:
   // Observer interface for monitoring ExtensionPrefValueMap.
   class Observer {
    public:
-    virtual ~Observer() {}
-
     // Called when the value for the given |key| set by one of the extensions
     // changes. This does not necessarily mean that the effective value has
     // changed.
     virtual void OnPrefValueChanged(const std::string& key) = 0;
     // Notification about the ExtensionPrefValueMap being fully initialized.
     virtual void OnInitializationCompleted() = 0;
     // Called when the ExtensionPrefValueMap is being destroyed. When called,
     // observers must unsubscribe.
     virtual void OnExtensionPrefValueMapDestruction() = 0;
+
+   protected:
+    virtual ~Observer() {}
   };
 
   ExtensionPrefValueMap();
   virtual ~ExtensionPrefValueMap();
 
   // ProfileKeyedService implementation.
   virtual void Shutdown() OVERRIDE;
 
   // Set an extension preference |value| for |key| of extension |ext_id|.
   // Takes ownership of |value|.
@@ skipping 98 matching lines @@
   // being destroyed. In tests, it isn't called, so the notification must
   // be done in the destructor. This bit tracks whether it has been done yet.
   bool destroyed_;
 
   ObserverList<Observer, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionPrefValueMap);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_PREF_VALUE_MAP_H_