ackChatMessage(chatGroupId, chatId, timestamp) {
		this.user._sendUnified('ChatRoom.AckChatMessage#1', {
			chat_group_id: chatGroupId,
			chat_id: chatId,
			timestamp: convertDateToUnix(timestamp)
		});
	}
Acknowledge (mark as read) a chat room.
@param {int} chatGroupId
@param {int} chatId
@param {Date|int} timestamp - The timestamp of the newest message you're acknowledging (will ack all older messages)