RefCounted types should not have public destructors, base/ edition

base/files/file_path_watcher.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.
 
 // This module provides a way to monitor a file or directory for changes.
 
 #ifndef BASE_FILES_FILE_PATH_WATCHER_H_
 #define BASE_FILES_FILE_PATH_WATCHER_H_
 #pragma once
 
@@ skipping 15 matching lines @@
 // detect the creation and deletion of files in a watched directory, but will
 // not detect modifications to those files. See file_path_watcher_mac.cc for
 // details.
 class BASE_EXPORT FilePathWatcher {
  public:
   // Declares the callback client code implements to receive notifications. Note
   // that implementations of this interface should not keep a reference to the
   // 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.
   // TODO(jhawkins): Move this into its own file. Also fix the confusing naming
   // wrt Delegate vs PlatformDelegate.
   class PlatformDelegate : public base::RefCountedThreadSafe<PlatformDelegate> {
    public:
     PlatformDelegate();
 
     // Start watching for the given |path| and notify |delegate| about changes.
@@ skipping 57 matching lines @@
  private:
   scoped_refptr<PlatformDelegate> impl_;
 
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 };
 
 }  // namespace files
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_PATH_WATCHER_H_