Service Worker Cache: cache.match() should resolve to undefined if no match

Spec was updated: since match failure is not an exceptional case,
the promise should fulfill, not reject.

https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#cache-match

BUG=428486
R=jkarlin

Review URL: https://codereview.chromium.org/693603002

git-svn-id: svn://svn.chromium.org/blink/trunk@184679 bbb929c8-8fbe-4397-9dbb-9b2b20218538