Service Worker: Offline mode for assetGroups works unstable #19490

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

After page loaded and assets pre-cached, go to offline (via devtools or turn off wi-fi). Load the same page on other page or click "Reload" in browser - there will be a message "This site can’t be reached". In some random combinations of offline modes/browser unloads/tabs manipulations you can get the cached version. But after you click "Reload" it disappears again.

Expected behavior

Check lodash.com. Once its service worker got a control and cached assets - it stable works offline, you can reload the page, navigate to subpages.

Minimal reproduction of the problem with instructions

https://ngsw.surge.sh
or
https://pwa-workshop-angular.firebaseapp.com
Load page, go to offline, click "Reload" in browser.

Source: https://github.com/webmaxru/pwatter/tree/ngsw

CC: @alxhub

What is the motivation / use case for changing the behavior?

Fix the bug

Environment

Angular version: 5.0.0.rc.0


Browser:
- [x] Chrome (desktop) version 61