(Filing bug from alchemist@)
It seems that some fetch calls to web_accessible_resources are still not working for Extension SW.

Steps:
1) from extension, register a SW to intercept fetch:
manifest.json:
..
"web_accessible_resources": ["war.html"],

background.js: 
navigator.serviceWorker.register('/sw.js');

sw.js:
self.addEventListener('fetch', event => {
  console.log('FETCH: ' + event.request.url);  // #XYZ
  if (event.request.url.endsWith('war.html')) {
    event.respondWith(new Response('sw content'));
  }
});

2) from page, fetch() a WAR, e.g.:
fetch('chrome-extension://abcd.../war.html').then(...);


Fetch handler in #XYZ above does not see war.html
Same goes with XHR.

However, if I load the resource through an iframe element in the page in step 2, fetch handler seems to see that. This was fixed in https://codereview.chromium.org/1532633003 & https://bugs.chromium.org/p/chromium/issues/detail?id=567382, but fetch/xhr still doesn't work.