WebIDE asks for confirmation to leave the page when committing and creating a new MR

Summary

WebIDE asks for confirmation to leave the page when committing and creating a new MR.

Steps to reproduce

1. Open a file in the WebIDE
2. Make some changes
3. Click the Commit button
4. Check the Start a new merge request checkbox
5. Click the Stage & Commit button

What is the current bug behavior?

Browser asks for confirmation to leave the page.

What is the expected correct behavior?

Browser should only ask for confirmation to leave the page when there are uncommitted changes.

Relevant logs and/or screenshots

The dialog is controlled by the browser, in Firefox it looks like this:

Output of checks

This bug happens on GitLab.com

Possible fixes

We register a window.onbeforeunload handler at https://gitlab.com/gitlab-org/gitlab-ce/blob/6fd2cef0461bfba50fb1d1346c12a47053ec344f/app/assets/javascripts/ide/components/ide.vue#L58, which checks this.someUncommittedChanges to decide if the dialog should be triggered or not. There might be a timing problem where the redirect to the MR form is triggered before this status is updated.