UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36

Steps to reproduce the problem:
1. Open a page from the extension 
2. Update the extension through developer dashboard
3. Wait for chrome to download the update and auto-restart the extension, automatically closing the extension pages

What is the expected behavior?
The extension should not restart automatically when an update is available, if the background script is persistent, or the extension has an active open tab (chrome-extensions://)

What went wrong?
As it says in the documentation, active extensions (those with persistent background scripts) do not automatically restart when there is an update available. However this is not the case as we have observed in our extension (attached link).

Our users are complaining that the extension restarts even though there are pages open (chrome-extension://) and the background page is active. We know that the background page is active because we even explicitly added "persistent: true" to our manifest.json. We're also sure that the background script is active since we even added a setInterval on it just to be sure.

But after all that, extension still restarted automatically, even happened to me.

To make things worse, an extension restart / closing of extension tabs now doesn't recognize window.onbeforeunload which previously dealth with this situation.

Original doc:
https://developer.chrome.com/extensions/runtime#event-onUpdateAvailable

WebStore page: https://chrome.google.com/webstore/detail/kancolle-command-center-%E6%94%B9/hkgmldnainaglpjngpajnnjfhpdjkohh

Did this work before? No 

Chrome version: 55.0.2883.87  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: Shockwave Flash 24.0 r0