Remove base::NonThreadSafe now that all users are gone!!

base/threading/non_thread_safe_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_THREADING_NON_THREAD_SAFE_IMPL_H_
-#define BASE_THREADING_NON_THREAD_SAFE_IMPL_H_
-
-#include "base/base_export.h"
-#include "base/threading/thread_checker_impl.h"
-
-namespace base {
-
-// Full implementation of NonThreadSafe, for debug mode or for occasional
-// temporary use in release mode e.g. when you need to CHECK on a thread
-// bug that only occurs in the wild.
-//
-// Note: You should almost always use the NonThreadSafe class to get
-// the right version of the class for your build configuration.
-class BASE_EXPORT NonThreadSafeImpl {
- public:
-  bool CalledOnValidThread() const;
-
- protected:
-  ~NonThreadSafeImpl();
-
-  // Changes the thread that is checked for in CalledOnValidThread. The next
-  // call to CalledOnValidThread will attach this class to a new thread. It is
-  // up to the NonThreadSafe derived class to decide to expose this or not.
-  // This may be useful when an object may be created on one thread and then
-  // used exclusively on another thread.
-  void DetachFromThread();
-
- private:
-  ThreadCheckerImpl thread_checker_;
-};
-
-}  // namespace base
-
-#endif  // BASE_THREADING_NON_THREAD_SAFE_IMPL_H_