Prevent user from closing browser tab with not submitted review comments

Problem to solve

The review feature is awesome! But I sometimes forget to press "Submit review" button before leaving merge request page. That causes unnecessary cycle when author asks me to submit my comments and I do so which leads to delay(sometimes up to a full day due to time-zone differences).

Intended users

Proposal

Google Music shows me confirm dialog when I try to close the tab with playing music:

I think as MVC we can do the same if there are not submitted review comments.

What does success look like, and how can we measure that?

A slightly shorter merge cycle time for gitlab-org?