RefCounted types should not have public destructors, base/ edition

base/files/file_path_watcher.h

Index: base/files/file_path_watcher.h
diff --git a/base/files/file_path_watcher.h b/base/files/file_path_watcher.h
index 3174a9e0ac9069037151b616839aa789cd1ab5e1..82e2445aeb0fa961dd2afd925922a68a90e6bd36 100644
--- a/base/files/file_path_watcher.h
+++ b/base/files/file_path_watcher.h
@@ -33,11 +33,16 @@ class BASE_EXPORT FilePathWatcher {
   // corresponding FileWatcher object to prevent a reference cycle.
   class Delegate : public base::RefCountedThreadSafe<Delegate> {
    public:
-    virtual ~Delegate() {}
     virtual void OnFilePathChanged(const FilePath& path) = 0;
     // Called when platform specific code detected an error. The watcher will
     // not call OnFilePathChanged for future changes.
     virtual void OnFilePathError(const FilePath& path) {}
+
+   protected:
+    virtual ~Delegate() {}
+
+   private:
+    friend class base::RefCountedThreadSafe<Delegate>;
   };
 
   // Used internally to encapsulate different members on different platforms.