code: void add0(PoolChunk<T> chunk) {
          chunk.parent = this;
          if (head == null) {
              head = chunk;
              chunk.prev = null;
              chunk.next = null;
          } else {
              chunk.prev = null;
              chunk.next = head;
              head.prev = chunk;
              head = chunk;
          }
      }
docs: Adds the {@link PoolChunk} to this {@link PoolChunkList}.