Objects that derive from RefCounted/RefCountedThreadSafe should not have public dtors.

base/message_loop_proxy_impl.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 BASE_MESSAGE_LOOP_PROXY_IMPL_H_
 #define BASE_MESSAGE_LOOP_PROXY_IMPL_H_
 #pragma once
 
 #include "base/base_export.h"
 #include "base/message_loop.h"
 #include "base/message_loop_proxy.h"
 #include "base/synchronization/lock.h"
 
 namespace base {
 
 // A stock implementation of MessageLoopProxy that is created and managed by a
 // MessageLoop. For now a MessageLoopProxyImpl can only be created as part of a
 // MessageLoop.
-class BASE_EXPORT MessageLoopProxyImpl
-    : public MessageLoopProxy {
+class BASE_EXPORT MessageLoopProxyImpl : public MessageLoopProxy {
  public:
-  virtual ~MessageLoopProxyImpl();
-
   // MessageLoopProxy implementation
   virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
                                const base::Closure& task,
                                int64 delay_ms) OVERRIDE;
   virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
                                const base::Closure& task,
                                base::TimeDelta delay) OVERRIDE;
   virtual bool PostNonNestableDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
       int64 delay_ms) OVERRIDE;
   virtual bool PostNonNestableDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
       base::TimeDelta delay) OVERRIDE;
   virtual bool RunsTasksOnCurrentThread() const OVERRIDE;
 
  protected:
+  virtual ~MessageLoopProxyImpl();
+
   // Override OnDestruct so that we can delete the object on the target message
   // loop if it still exists.
   virtual void OnDestruct() const OVERRIDE;
 
  private:
+  // Allow the MessageLoop to create a MessageLoopProxyImpl.
+  friend class ::MessageLoop;
+  friend class DeleteHelper<MessageLoopProxyImpl>;
+
   MessageLoopProxyImpl();
 
   // Called directly by MessageLoop::~MessageLoop.
   virtual void WillDestroyCurrentMessageLoop();
 
 
   bool PostTaskHelper(const tracked_objects::Location& from_here,
                       const base::Closure& task,
                       base::TimeDelta delay,
                       bool nestable);
 
-  // Allow the messageLoop to create a MessageLoopProxyImpl.
-  friend class ::MessageLoop;
-
   // The lock that protects access to target_message_loop_.
   mutable base::Lock message_loop_lock_;
   MessageLoop* target_message_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageLoopProxyImpl);
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_PROXY_IMPL_H_