@Override
  public boolean putObject(String key, AmbryCacheEntry value) {
    if (super.putObject(key, value)) {
      putObjectCountDown.countDown();
      return true;
    }
    return false;
  }
Constructs an instance of AmbryCache
@param cacheId String identifier for this cache
@param cacheEnabled Toggles cache. If true, cache is enabled. Else, cache is disabled.
@param maxNumCacheEntries Maximum number of cache entries
@param metricRegistry Instance of metrics registry to record stats
ambry-router/src/test/java/com/github/ambry/router/AmbryCacheWithStats.java