Modify ThreadChecker and NonThreadSafe so that their functionality is

base/threading/thread_checker_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_THREAD_CHECKER_IMPL_H_
+#define BASE_THREADING_THREAD_CHECKER_IMPL_H_
+#pragma once
+
+#include "base/synchronization/lock.h"
+#include "base/threading/platform_thread.h"
+
+namespace base {
+
+// Real implementation of ThreadChecker, for use in debug mode, or
+// for temporary use in release mode (e.g. to CHECK on a threading issue
+// seen only in the wild).
+//
+// Note: You should almost always use the ThreadChecker class to get the
+// right version for your build configuration.
+class ThreadCheckerImpl {
+ public:
+  ThreadCheckerImpl();
+  ~ThreadCheckerImpl();
+
+  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 base::Lock lock_;
+  // This is mutable so that CalledOnValidThread can set it.
+  // It's guarded by |lock_|.
+  mutable PlatformThreadId valid_thread_id_;
+};
+
+}  // namespace base
+
+#endif  // BASE_THREADING_THREAD_CHECKER_IMPL_H_