Modify ThreadChecker and NonThreadSafe so that their functionality is

base/threading/non_thread_safe.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_THREADING_NON_THREAD_SAFE_H_
 #define BASE_THREADING_NON_THREAD_SAFE_H_
 #pragma once
 
-#include "base/threading/thread_checker.h"
+#ifndef NDEBUG
+#include "base/threading/non_thread_safe_impl.h"
+#endif
 
 namespace base {
 
-// A helper class used to help verify that methods of a class are
-// called from the same thread.  One can inherit from this class and use
-// CalledOnValidThread() to verify.
+// Do nothing implementation of NonThreadSafe, for release mode.
+//
+// Note: You should almost always use the NonThreadSafe class to get
+// the right version of the class for your build configuration.
+class NonThreadSafeDoNothing {
+ public:
+  bool CalledOnValidThread() const {
+    return true;
+  }
+
+ protected:
+  void DetachFromThread() {}
+};
+
+// NonThreadSafe is a helper class used to help verify that methods of a
+// class are called from the same thread.  One can inherit from this class
+// and use CalledOnValidThread() to verify.
 //
 // This is intended to be used with classes that appear to be thread safe, but
 // aren't.  For example, a service or a singleton like the preferences system.
 //
 // Example:
 // class MyClass : public base::NonThreadSafe {
 //  public:
 //   void Foo() {
 //     DCHECK(CalledOnValidThread());
 //     ... (do stuff) ...
 //   }
 // }
 //
 // In Release mode, CalledOnValidThread will always return true.
 //
 #ifndef NDEBUG
-class NonThreadSafe {
- public:
-  ~NonThreadSafe();
-
-  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:
-  ThreadChecker thread_checker_;
+class NonThreadSafe : public NonThreadSafeImpl {
 };
 #else
-// Do nothing in release mode.
-class NonThreadSafe {
- public:
-  bool CalledOnValidThread() const {
-    return true;
-  }
-
- protected:
-  void DetachFromThread() {}
+class NonThreadSafe : public NonThreadSafeDoNothing {
 };
 #endif  // NDEBUG
 
 }  // namespace base
 
 #endif  // BASE_NON_THREAD_SAFE_H_