hide DnsCache's constructor and deconstructor

src/manager/DnsCache.cc

@@ -108,3 +108,11 @@ void DnsCache::del(const DnsCache::HostPort& key)
 	cache_pool_.del(key);
 }
 
+DnsCache::DnsCache()
+{
+}
+
+DnsCache::~DnsCache()
+{
+}
+

src/manager/DnsCache.h

@@ -151,6 +151,11 @@ private:
 	};
 
 	LRUCache<HostPort, DnsCacheValue, ValueDeleter> cache_pool_;
+
+public:
+	// To prevent inline calling LRUCache's constructor and deconstructor.
+	DnsCache();
+	~DnsCache();
 };
 
 #endif