Modify ThreadChecker and NonThreadSafe so that their functionality is

base/threading/non_thread_safe_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_THREADING_NON_THREAD_SAFE_IMPL_H_
+#define BASE_THREADING_NON_THREAD_SAFE_IMPL_H_
+#pragma once
+
+#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 NonThreadSafeImpl {
+ public:
+  ~NonThreadSafeImpl();
+
+  bool CalledOnValidThread() const;
+
+ protected:
+  // 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_