Move platform_thread to base/threading and put in the base namespace. I left ...

base/thread_checker.h

-// Copyright (c) 2010 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_THREAD_CHECKER_H_
-#define BASE_THREAD_CHECKER_H_
-#pragma once
-
-#ifndef NDEBUG
-#include "base/lock.h"
-#include "base/platform_thread.h"
-#endif // NDEBUG
-
-// Before using this class, please consider using NonThreadSafe as it
-// makes it much easier to determine the nature of your class.
-//
-// A helper class used to help verify that some methods of a class are
-// called from the same thread.  One can inherit from this class and use
-// CalledOnValidThread() to verify.
-//
-// Inheriting from class indicates that one must be careful when using the class
-// with multiple threads. However, it is up to the class document to indicate
-// how it can be used with threads.
-//
-// Example:
-// class MyClass : public ThreadChecker {
-//  public:
-//   void Foo() {
-//     DCHECK(CalledOnValidThread());
-//     ... (do stuff) ...
-//   }
-// }
-//
-// In Release mode, CalledOnValidThread will always return true.
-//
-#ifndef NDEBUG
-class ThreadChecker {
- public:
-  ThreadChecker();
-  ~ThreadChecker();
-
-  bool CalledOnValidThread() const;
-
-  // Changes the thread that is checked for in CalledOnValidThread.  This may
-  // be useful when an object may be created on one thread and then used
-  // exclusively on another thread.
-  void DetachFromThread();
-
- private:
-  void EnsureThreadIdAssigned() const;
-
-  mutable Lock lock_;
-  // This is mutable so that CalledOnValidThread can set it.
-  // It's guarded by |lock_|.
-  mutable PlatformThreadId valid_thread_id_;
-};
-#else
-// Do nothing in release mode.
-class ThreadChecker {
- public:
-  bool CalledOnValidThread() const {
-    return true;
-  }
-
-  void DetachFromThread() {}
-};
-#endif  // NDEBUG
-
-#endif  // BASE_THREAD_CHECKER_H_