DevTools: Shows "(from ServiceWorker)" message instead of "(from cache)" when
the request is served from the ServiceWorker.

BUG=401389
TEST=N/A

Review URL: https://codereview.chromium.org/482423003

git-svn-id: svn://svn.chromium.org/blink/trunk@180705 bbb929c8-8fbe-4397-9dbb-9b2b20218538