https://chrome.google.com/webstore/detail/ngadjednajjomdjagknebelhmcjggklk
There it is. It shows width, height and file size(which you can turn off) in a corner. It looks neat from the box, but you still can configure it for yourself. I would appreciate any feedback.Also, there's source available at https://github.com/KiDoki/Image-Resolution
If there's any interest, I will continue working on it.