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"
 
 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.
+class NonThreadSafeImpl;
+class NonThreadSafeDoNothing;
+
+// 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 {
+typedef NonThreadSafeImpl NonThreadSafe;
+#else
+typedef NonThreadSafeDoNothing NonThreadSafe;
+#endif  // NDEBUG
+
+// 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 typedef to get
+// the right version of the class.
+class NonThreadSafeImpl {
  public:
-  ~NonThreadSafe();
+  ~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:
-  ThreadChecker thread_checker_;
+  ThreadCheckerImpl thread_checker_;
 };
-#else
-// Do nothing in release mode.
-class NonThreadSafe {
+
+// Do nothing implementation of NonThreadSafe, for release mode.
+//
+// Note: You should almost always use the NonThreadSafe typedef to get
+// the right version of the class.
+class NonThreadSafeDoNothing {
  public:
   bool CalledOnValidThread() const {
     return true;
   }
 
  protected:
   void DetachFromThread() {}
 };
-#endif  // NDEBUG
 
 }  // namespace base
 
 #endif  // BASE_NON_THREAD_SAFE_H_