Fix race condition in Directory.create.

runtime/bin/directory_win.cc

Index: runtime/bin/directory_win.cc
diff --git a/runtime/bin/directory_win.cc b/runtime/bin/directory_win.cc
index 4d8c9fa8f1d02040f66a02776d57cc9eefc61ba8..9d8f6f31935d30691c4344acc8354d300dfef835 100644
--- a/runtime/bin/directory_win.cc
+++ b/runtime/bin/directory_win.cc
@@ -344,13 +344,14 @@ char* Directory::Current() {
 
 bool Directory::Create(const char* dir_name) {
   const wchar_t* system_name = StringUtils::Utf8ToWide(dir_name);
-  // If the directory already exists and is a directory do not
-  // attempt to create it again and treat it as a success.
-  if (ExistsHelper(system_name) == EXISTS) {
+  int create_status = CreateDirectoryW(system_name, NULL);
+  // If the directory already existed, treat it as a success.
+  if (create_status == 0 &&
+      GetLastError() == ERROR_ALREADY_EXISTS &&
+      ExistsHelper(system_name) == EXISTS) {
     free(const_cast<wchar_t*>(system_name));
     return true;
   }
-  int create_status = CreateDirectoryW(system_name, NULL);
   free(const_cast<wchar_t*>(system_name));
   return (create_status != 0);
 }