message: Update file_system.cc
diff: @@ -308,8 +308,8 @@ StringPiece FileSystem::Basename(StringPiece path) const {
  StringPiece FileSystem::Extension(StringPiece path) const {
  StringPiece basename = this->Basename(path);
  - int pos = basename.rfind('.');
  - if (static_cast<size_t>(pos) == StringPiece::npos) {
  + size_t pos = basename.rfind('.');
  + if (pos == StringPiece::npos) {
  return StringPiece(path.data() + path.size(), 0);
  } else {
  return StringPiece(path.data() + pos + 1, path.size() - (pos + 1));
  