成员的完整列表，这些成员属于 AgoraChatMessageStatistics,包括所有继承而来的类成员

	attachmentSize	AgoraChatMessageStatistics
	chatType	AgoraChatMessageStatistics
	direction	AgoraChatMessageStatistics
	from	AgoraChatMessageStatistics
	messageId	AgoraChatMessageStatistics
	messageSize	AgoraChatMessageStatistics
	thumbnailSize	AgoraChatMessageStatistics
	timestamp	AgoraChatMessageStatistics
	to	AgoraChatMessageStatistics
	type	AgoraChatMessageStatistics