Named an unnamed thread in ObserverManager

Summary: This patch names the thread inside `ObserverManager::NextQueue`, similar to the vector of threads in `ObserverManager::CurrentQueue`.

Reviewed By: yfeldblum

Differential Revision: D15746165

fbshipit-source-id: 02df5616dcc2af27f318088c051a49d14df9a4df

folly/experimental/observer/detail/ObserverManager.cpp

@@ -99,6 +99,9 @@ class ObserverManager::NextQueue {
  public:
   explicit NextQueue(ObserverManager& manager) : manager_(manager) {
     thread_ = std::thread([&]() {
+      folly::setThreadName(
+          folly::sformat("{}NQ", kObserverManagerThreadNamePrefix));
+
       Core::WeakPtr queueCoreWeak;
 
       while (true) {