Add comments about threadSafeBind()

Source/wtf/Functional.h

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 20 matching lines @@
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 #include "wtf/ThreadSafeRefCounted.h"
 #include "wtf/WeakPtr.h"
 
 namespace WTF {
 
 // Functional.h provides a very simple way to bind a function pointer and arguments together into a function object
 // that can be stored, copied and invoked, similar to how boost::bind and std::bind in C++11.
 
+// Use threadSafeBind() or createCrossThreadTask() if the function/task is
+// called on a (potentially) different thread from the current thread.
+
 // A FunctionWrapper is a class template that can wrap a function pointer or a member function pointer and
 // provide a unified interface for calling that function.
 template<typename>
 class FunctionWrapper;
 
 // Bound static functions:
 template<typename R, typename... P>
 class FunctionWrapper<R(*)(P...)> {
 public:
     typedef R ResultType;
@@ skipping 310 matching lines @@
 
 typedef Function<void()> Closure;
 
 }
 
 using WTF::Function;
 using WTF::bind;
 using WTF::Closure;
 
 #endif // WTF_Functional_h