Modify ThreadChecker and NonThreadSafe so that their functionality is

base/threading/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_THREADING_THREAD_CHECKER_H_
 #define BASE_THREADING_THREAD_CHECKER_H_
 #pragma once
 
-#ifndef NDEBUG
 #include "base/synchronization/lock.h"
 #include "base/threading/platform_thread.h"
-#endif // NDEBUG
 
 namespace base {
 
+class ThreadCheckerImpl;
+class ThreadCheckerDoNothing;
+
 // 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.
+// ThreadChecker is 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.
+// 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
+typedef ThreadCheckerImpl ThreadChecker;
+#else
+typedef ThreadCheckerDoNothing ThreadChecker;
+#endif  // NDEBUG
+
+// Real implementation, 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).
 //
-#ifndef NDEBUG
-class ThreadChecker {
+// Note: You should almost always use the ThreadChecker typedef to get the
+// right version.
+class ThreadCheckerImpl {
  public:
-  ThreadChecker();
-  ~ThreadChecker();
+  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_;
 };
-#else
-// Do nothing in release mode.
-class ThreadChecker {
+
+// Do nothing implementation, for use in release mode.
+//
+// Note: You should almost always use the ThreadChecker typedef to get the
+// right version.
+class ThreadCheckerDoNothing {
  public:
   bool CalledOnValidThread() const {
     return true;
   }
 
   void DetachFromThread() {}
 };
-#endif  // NDEBUG
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_CHECKER_H_