Automatically reconnect on offline event

[msujew]

What it does

Fixes #9298.

As the bug report over at chromium indicates, listening to the offline event of the browser enables us to manually tell the socket to reconnect. This event is usually fired during a change of network.

I tested this behavior on an Ubuntu 20.04 machine. Running a VM on Windows 10 didn't allow me to reproduce the network issue. I also looked for any regression issues under Firefox and Windows, but everything seems to work normally even with the fix in place.

How to test

1. Start Theia in a chromium based browser on a Linux distribution.
2. Change to another Wifi network.
3. The websocket connection will be re-established, indicated by the banner changing from online to offline and finally back to online.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[paul-marechal]

Code LGTM. Although I wasn't able to reproduce the issue on master using Linux and Chrome. It is working for me with and without this change.

[vince-fugnitto]

Code LGTM. Although I wasn't able to reproduce the issue on master using Linux and Chrome. It is working for me with and without this change.

I was unable to reproduce the issue as well on both master and this pull-request.

[paul-marechal]

@Darkgaja can you confirm that you have the issue as of master and that this PR fixes it for you? I don't see any regression, so if it fixes it for you then I'll merge.

[msujew]

@marechal-p @vince-fugnitto Just tested it on the master and the issue still persists:

2021-04-13_08-46-40.mp4

(Saving doesn't work, git synchronisation as well. Waiting doesn't help)

My changes seem to fix these issues:

2021-04-13_11-15-32.mp4

[vince-fugnitto]

@Darkgaja thank you for providing the screenshares, they helped me reproduce the issue on master and I confirmed that the pull-request addresses the issue nicely 👍