Add support for base::Closure in the MessageLoop.

base/bind_internal_win.h.pump

 $$ This is a pump file for generating file templates.  Pump is a python
 $$ script that is part of the Google Test suite of utilities.  Description
 $$ can be found here:
 $$
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 $$
 
 $var MAX_ARITY = 6
 
 // Copyright (c) 2011 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.
 
 // Specializations of FunctionTraits<> for Windows specific calling
 // conventions.  Please see base/bind_internal.h for more info.
 
 #ifndef BASE_BIND_INTERNAL_WIN_H_
 #define BASE_BIND_INTERNAL_WIN_H_
 #pragma once
 
+// In the x64 architecture in Windows, __fastcall, __stdcall, etc, are all
+// the same as __cdecl which would turn the following specializations into
+// multiple definitions.
+#if !defined(ARCH_CPU_X86_64)
+
 namespace base {
 namespace internal {
 
 template <typename Sig>
 struct FunctionTraits;
 
 $range ARITY 0..MAX_ARITY
 $for ARITY [[
 $range ARG 1..ARITY
 
@@ skipping 31 matching lines @@
 
 ]]  $$ for ARG
 ]]  $$ if ARITY > 0
 };
 
 ]]  $$for ARITY
 
 }  // namespace internal
 }  // namespace base
 
+#endif  // !defined(ARCH_CPU_X86_64)
+
 #endif  // BASE_BIND_INTERNAL_WIN_H_