Modify ThreadChecker and NonThreadSafe so that their functionality is

base/threading/thread_checker.h

Index: base/threading/thread_checker.h
diff --git a/base/threading/thread_checker.h b/base/threading/thread_checker.h
index 712b5b56f03efeb429dd9231bfc8807a99c0dc32..33b6764e966b269bfceadeba4ad94b8ce4d0bc32 100644
--- a/base/threading/thread_checker.h
+++ b/base/threading/thread_checker.h
@@ -7,22 +7,34 @@
 #pragma once
 
 #ifndef NDEBUG
-#include "base/synchronization/lock.h"
-#include "base/threading/platform_thread.h"
-#endif // NDEBUG
+#include "base/threading/thread_checker_impl.h"
+#endif
 
 namespace base {
 
+// Do nothing implementation, for use in release mode.
+//
+// Note: You should almost always use the ThreadChecker class to get the
+// right version for your build configuration.
+class ThreadCheckerDoNothing {
+ public:
+  bool CalledOnValidThread() const {
+    return true;
+  }
+
+  void DetachFromThread() {}
+};
+
 // 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 {
@@ -34,37 +46,11 @@ namespace base {
 // }
 //
 // In Release mode, CalledOnValidThread will always return true.
-//
 #ifndef NDEBUG
-class ThreadChecker {
- public:
-  ThreadChecker();
-  ~ThreadChecker();
-
-  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_;
+class ThreadChecker : public ThreadCheckerImpl {
 };
 #else
-// Do nothing in release mode.
-class ThreadChecker {
- public:
-  bool CalledOnValidThread() const {
-    return true;
-  }
-
-  void DetachFromThread() {}
+class ThreadChecker : public ThreadCheckerDoNothing {
 };
 #endif  // NDEBUG