Add MessageLoopProxy::current

base/message_loop_proxy_impl.h

 // Copyright (c) 2011 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 takes in a MessageLoop
-// and keeps track of its lifetime using the MessageLoop DestructionObserver.
-// For now a MessageLoopProxyImpl can only be created for the current thread.
+// 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,
-      public MessageLoop::DestructionObserver {
+    : public MessageLoopProxy {
  public:
   virtual ~MessageLoopProxyImpl();
 
   // MessageLoopProxy implementation
   virtual bool PostTask(const tracked_objects::Location& from_here,
                         Task* task);
   virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
                                Task* task,
                                int64 delay_ms);
   virtual bool PostNonNestableTask(const tracked_objects::Location& from_here,
                                    Task* task);
   virtual bool PostNonNestableDelayedTask(
       const tracked_objects::Location& from_here,
       Task* task,
       int64 delay_ms);
   virtual bool PostTask(const tracked_objects::Location& from_here,
                         const base::Closure& task);
   virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
                                const base::Closure& task,
                                int64 delay_ms);
   virtual bool PostNonNestableTask(const tracked_objects::Location& from_here,
                                    const base::Closure& task);
   virtual bool PostNonNestableDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
       int64 delay_ms);
   virtual bool BelongsToCurrentThread();
 
-  // MessageLoop::DestructionObserver implementation
-  virtual void WillDestroyCurrentMessageLoop();
-
  protected:
   // Override OnDestruct so that we can delete the object on the target message
   // loop if it still exists.
   virtual void OnDestruct() const;
 
  private:
   MessageLoopProxyImpl();
+
+  // Called directly by MessageLoop::~MessageLoop.
+  virtual void WillDestroyCurrentMessageLoop();
+
+
   // TODO(ajwong): Remove this after we've fully migrated to base::Closure.
   bool PostTaskHelper(const tracked_objects::Location& from_here,
                       Task* task,
                       int64 delay_ms,
                       bool nestable);
   bool PostTaskHelper(const tracked_objects::Location& from_here,
                       const base::Closure& task,
                       int64 delay_ms,
                       bool nestable);
 
-  // For the factory method to work
-  friend class MessageLoopProxy;
+  // 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_