show progress bar for download files

1. User1 add big file (apk for example) to room
1. User2 try save this file to "Download" dir
1. When User2 try save big file from room (or from files list of room) - pressing on "save button" - not show any changes.
1. User2 press to save button some count...
1. After some time (when file downloaded) - element show more dialogs with "save file"

It is good idea, that element will show some progress bar for downloading file. And with that dialog user will undestand, that file is big, it downloading and it must be wait.