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

chrome/installer/util/install_util.cc

Index: chrome/installer/util/install_util.cc
===================================================================
--- chrome/installer/util/install_util.cc	(revision 80528)
+++ chrome/installer/util/install_util.cc	(working copy)
@@ -136,15 +136,14 @@
 }
 
 bool InstallUtil::IsOSSupported() {
-  int major, minor;
   base::win::Version version = base::win::GetVersion();
-  base::win::GetServicePackLevel(&major, &minor);
+  const int* service_pack = base::win::OSInfo::GetInstance()->service_pack();
 
   // We do not support Win2K or older, or XP without service pack 2.
   VLOG(1) << "Windows Version: " << version
-          << ", Service Pack: " << major << "." << minor;
+          << ", Service Pack: " << service_pack[0] << "." << service_pack[1];
   return (version > base::win::VERSION_XP) ||
-      (version == base::win::VERSION_XP && major >= 2);
+      (version == base::win::VERSION_XP && service_pack[0] >= 2);
 }
 
 void InstallUtil::WriteInstallerResult(bool system_install,