Expose stats from object cache to MultiLevelObjectCache.

Summary: As title. Allow stats to be accessed from MultiLevelObjectCache

Reviewed By: byahn0996

Differential Revision: D73687059

fbshipit-source-id: b0aee094749bd86c4ff085151549efc09ec291c2

Author: haowu14

cachelib/object_cache/ObjectCacheBase.h

@@ -26,6 +26,7 @@ namespace objcache2 {
 
 template <typename AllocatorT>
 class ObjectCacheBase : public CacheBase {
+ public:
   // Get a string referring to the cache name for this cache
   const std::string getCacheName() const override {
     return l1Cache_->getCacheName();