Rename url to scriptURL and remove scope from ServiceWorker

Alignment with the latest spec changes:
https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#service-worker-obj

BUG=399516
R=dominicc@chromium.org

Review URL: https://codereview.chromium.org/433513010

git-svn-id: svn://svn.chromium.org/blink/trunk@179455 bbb929c8-8fbe-4397-9dbb-9b2b20218538