Roll forward up to cl/355978895.

cpp/platform/base/feature_flags.h

@@ -18,6 +18,9 @@ class FeatureFlags {
     // ServiceController is released to prevent calls to that API from
     // other threads.
     bool disable_released_service_controller = true;
+    // Ignore subsequent BWU Available events when we're still processing the
+    // first one.
+    bool disallow_out_of_order_bwu_avail_event = true;
   };
 
   static const FeatureFlags& GetInstance() {