This app was mentioned in 3 comments, with an average of 1.33 upvotes
For android developed by /u/60k_risk: https://play.google.com/store/apps/details?id=creativecoders.clashroyalchesttracker
For iOS developed by /u/TouchMint: https://itunes.apple.com/us/app/chest-tracker-for-clash-royale/id1091375358?mt=8
It allows you to track how many chests you received, and can then tell you which 4 chests you have coming next, assuming you have been keeping count of your chests thus far, as the chest drop is a sequence, not a % chance like a normal game.