Version: 51.0.2704.19 dev
OS: Linux

What steps will reproduce the problem?
(1) Go to https://jakearchibald.github.io/trained-to-thrill/
(2) Reload a few times and make sure SW is running and Cache Storage populated.
(3) Go to  DevTools → Resources → Cache Storage -> trains-data

What is the expected output?

Response field should be populated.

What do you see instead?

Response field is empty.

In Console I can see there's a response:

caches.open('trains-data').then(cache => mycache = cache);
mycache.keys().then(keys => key = keys[0])
key.url
=> "https://api.flickr.com/services/rest/?method=flickr.photos.search&extras=description&format=json&api_key=f2cca7d09b75c6cdea6864aca72e9895&text=train%20station&license=4%2C5%2C6%2C7&content_type=1&nojsoncallback=1&per_page=10"
mycache.match(key).then(r => console.log(r.status))
=> 200


Maybe something about CORS requests?