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

base/win/windows_version.cc

Index: base/win/windows_version.cc
===================================================================
--- base/win/windows_version.cc	(revision 79219)
+++ base/win/windows_version.cc	(working copy)
@@ -34,7 +34,7 @@
     } else if (version_info.dwMajorVersion == 6) {
       if (version_info.wProductType != VER_NT_WORKSTATION) {
         // 2008 is 6.0, and 2008 R2 is 6.1.
-        win_version = VERSION_2008;
+        win_version = VERSION_SERVER_2008;
       } else {
         if (version_info.dwMinorVersion == 0) {
           win_version = VERSION_VISTA;
@@ -69,7 +69,7 @@
 }
 
 WindowsArchitecture GetWindowsArchitecture() {
-  SYSTEM_INFO system_info;
+  SYSTEM_INFO system_info = {0};
   GetNativeSystemInfo(&system_info);
   switch (system_info.wProcessorArchitecture) {
     case PROCESSOR_ARCHITECTURE_INTEL: return X86_ARCHITECTURE;