RefCounted types should not have public destructors, delegate cleanup

chrome/browser/extensions/extension_pref_value_map.h

Index: chrome/browser/extensions/extension_pref_value_map.h
diff --git a/chrome/browser/extensions/extension_pref_value_map.h b/chrome/browser/extensions/extension_pref_value_map.h
index 2a168ad218b0c8e365d50522d0bf009e7b0fefe4..3b89d2b656ed2b1e5ac69e268bda48a775b8af2b 100644
--- a/chrome/browser/extensions/extension_pref_value_map.h
+++ b/chrome/browser/extensions/extension_pref_value_map.h
@@ -51,8 +51,6 @@ class ExtensionPrefValueMap : public ProfileKeyedService {
   // 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.
@@ -62,6 +60,9 @@ class ExtensionPrefValueMap : public ProfileKeyedService {
     // Called when the ExtensionPrefValueMap is being destroyed. When called,
     // observers must unsubscribe.
     virtual void OnExtensionPrefValueMapDestruction() = 0;
+
+   protected:
+    virtual ~Observer() {}
   };
 
   ExtensionPrefValueMap();