GitLab

Since the default behavior is to fallback to network, preventDefault()
should cause a network error.

As per spec: https://github.com/slightlyoff/ServiceWorker/issues/51
(see commit f022c3a6d)

Also add a test for calling FetchEvent.respondWith() with a rejected
promise; this must also produce a network error.

BUG=432825

Review URL: https://codereview.chromium.org/733983002

git-svn-id: svn://svn.chromium.org/blink/trunk@185451 bbb929c8-8fbe-4397-9dbb-9b2b20218538