Make the windows_version.h functions threadsafe by using a singleton.

base/win/windows_version.h

 // 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.
 
 #ifndef BASE_WIN_WINDOWS_VERSION_H_
 #define BASE_WIN_WINDOWS_VERSION_H_
 #pragma once
 
 typedef void* HANDLE;
 
 namespace base {
 namespace win {
 
 // NOTE: Keep these in order so callers can do things like
-// "if (GetWinVersion() > WINVERSION_2000) ...".  It's OK to change the values,
-// though.
+// "if (base::win::GetVersion() > base::win::VERSION_2000) ...".  It's OK to
+// change the values, though.
 enum Version {
   VERSION_PRE_2000 = 0,     // Not supported
   VERSION_2000 = 1,         // Not supported
   VERSION_XP = 2,
   VERSION_SERVER_2003 = 3,  // Also includes Windows XP Professional x64 edition
   VERSION_VISTA = 4,
-  VERSION_2008 = 5,
+  VERSION_SERVER_2008 = 5,
   VERSION_WIN7 = 6,
 };
 
 // Returns the running version of Windows.
 Version GetVersion();
 
 // Returns the major and minor version of the service pack installed.
 void GetServicePackLevel(int* major, int* minor);
 
 enum WindowsArchitecture {
@@ skipping 24 matching lines @@
 WOW64Status GetWOW64Status();
 
 // Like GetWOW64Status(), but for the supplied handle instead of the current
 // process.
 WOW64Status GetWOW64StatusForProcess(HANDLE process_handle);
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_WIN_WINDOWS_VERSION_H_