[ServiceWorker] Add LayoutTests for the fallback behavior of FetchEvent.

Currently the fallback behavior for redirect responses is not implemented correctly.
https://codereview.chromium.org/705273004/ will fix this problem.
This patch adds LayoutTests for this bug.

BUG=431985

Review URL: https://codereview.chromium.org/712303002

git-svn-id: svn://svn.chromium.org/blink/trunk@185185 bbb929c8-8fbe-4397-9dbb-9b2b20218538