Implement Counter Wrapper Classes

Summary:
This adds the `NullableStats` counter wrapper classes which wrap the `BaseStats` counter classes.

On counter initialization, NullableStats determines the name of the generated counter type and checks if this name is present in the MonitoringConfigLoader regex set. If the name is present, the class is just a passthrough to the BaseStats counter.

Otherwise, it implements a "dummy" counter class that won't instantiate the counter in Service Data and won't add any values when called. This is implemented slightly differently for each counter type due to the underlying counter class and how initialization occurs. But the end result is the same, if the counter name is not present in the monitoring config regex list, it will not be present locally in service data.

Reviewed By: jalopezsilva

Differential Revision: D50521531

fbshipit-source-id: 051089e7af2027a5260e918364fc9f07eaf9226d

proxygen/lib/stats/BaseStats.cpp

@@ -11,3 +11,8 @@
 DEFINE_bool(basestats_all_time_timeseries,
             false,
             "If true, BaseStats will use all-time aggregations");
+
+/*static*/
+bool proxygen::BaseStats::isAllTimeTimeseriesEnabled() {
+  return FLAGS_basestats_all_time_timeseries;
+}

proxygen/lib/stats/BaseStats.h

@@ -81,12 +81,16 @@ class BaseStats {
       tlStat->add(value);
     }
   }
-  static void incrementOptionalCounter(std::optional<TLCounter>& tlCounter,
+
+  template <typename StatT>
+  static void incrementOptionalCounter(std::optional<StatT>& tlCounter,
                                        facebook::fb303::CounterType value) {
     if (tlCounter) {
       tlCounter->incrementValue(value);
     }
   }
+
+  static bool isAllTimeTimeseriesEnabled();
 };
 
 } // namespace proxygen