ServiceWorker: Temporarily disable layout tests

These tests will be broken by [2] and re-enabled by [3].

[1] Blink: THIS PATCH
[2] Chromium: https://codereview.chromium.org/517493002/
[3] Blink: https://codereview.chromium.org/517223002/

BUG=406240
TEST=n/a
NOTRY=true

Review URL: https://codereview.chromium.org/524193003

git-svn-id: svn://svn.chromium.org/blink/trunk@181145 bbb929c8-8fbe-4397-9dbb-9b2b20218538