message: Fix warnings
  Summary:
  Extra `;`, shadowed declarations and unitialised variables
  were causing warnings to callers.
diff: @@ -23,7 +23,7 @@ namespace fb303 {
  namespace detail {
  template <typename ClockT>
  -static std::chrono::seconds statDuration(
  +std::chrono::seconds statDuration(
  const folly::Optional<std::chrono::seconds>& slidingWindowLength,
  typename ClockT::time_point creationTime) {
  auto now = ClockT::now();
  