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

sandbox/src/service_resolver_unittest.cc

Index: sandbox/src/service_resolver_unittest.cc
===================================================================
--- sandbox/src/service_resolver_unittest.cc	(revision 80667)
+++ sandbox/src/service_resolver_unittest.cc	(working copy)
@@ -120,7 +120,8 @@
 }
 
 sandbox::ServiceResolverThunk* GetTestResolver(bool relaxed) {
-  if (base::win::GetWOW64Status() == base::win::WOW64_ENABLED)
+  if (base::win::OSInfo::GetInstance()->wow64_status() ==
+      base::win::OSInfo::WOW64_ENABLED)
     return new Wow64ResolverTest(relaxed);
   if (!sandbox::IsXPSP2OrLater())
     return new Win2kResolverTest(relaxed);