[ServiceWorker] Serialize Cache.put() calls in Cache.match tests.

Also remove extraneous test cache entry.

The result of inserting cache entries that have 'Vary' headers depend on
the order of insertion. Make the test setup step be deterministic so
that the prepopulated cache is always in a predictable state when the
tests are run.

R=jsbell, bkelly@mozilla.com
BUG=428965,374802,429874

Review URL: https://codereview.chromium.org/705343002

git-svn-id: svn://svn.chromium.org/blink/trunk@185060 bbb929c8-8fbe-4397-9dbb-9b2b20218538