Tweak W3C test harness timeout for some Service Worker tests

These tests timeout on Win XP.  This patch changes the W3C timeout to be
shorter than run-webkit-tests, so the W3C harness can report which test
in the file timed out.

BUG=405847,401381

Review URL: https://codereview.chromium.org/492223002

git-svn-id: svn://svn.chromium.org/blink/trunk@180724 bbb929c8-8fbe-4397-9dbb-9b2b20218538