ServiceWorker: Tweak layout tests based on the latest install sequence

[1] Blink: https://codereview.chromium.org/524193003/
[2] Chromium: https://codereview.chromium.org/517493002/
[3] Blink: THIS PATCH


BUG=406240
TEST=run_webkit_tests.py --debug http/tests/serviceworker/

Review URL: https://codereview.chromium.org/517223002

git-svn-id: svn://svn.chromium.org/blink/trunk@181168 bbb929c8-8fbe-4397-9dbb-9b2b20218538