I have this on a new site / arcade I am currently putting together.
I couldnt find the exact thing I needed but found a module and have modified it to my requirements.
This offers Zoom In, Zoom Out, and Reset. Also set quality to Low, Medium, or High. It is in the side modules next to game.
You can see it in action at
http://www.jimclarke.co.uk/arcade.php You do however need to be registered to see the games.
If anyone wants a copy let me know. I have written some instructions to go with the files. If there is somewhere where I could give it a permanent home then let me know and I will write it up properly.