Identifier of the chat in which to count messages.
Filter for message content; searchMessagesFilterEmpty is unsupported in this function.
Optional
return_Pass true to get the number of messages without sending network requests, or -1 if the number of messages is unknown locally.
If not 0, only messages in the specified Saved Messages topic will be counted; pass 0 to count all messages, or for chats other than Saved Messages.
Returns approximate number of messages of the specified type in the chat. Request type for Tdjson#getChatMessageCount.