Implement navigator.serviceWorker interface

Replacing old navigator.registerServiceWorker

BUG=285976
TEST=http/tests/serviceworker/registration.html

Review URL: https://codereview.chromium.org/157523005

git-svn-id: svn://svn.chromium.org/blink/trunk@166980 bbb929c8-8fbe-4397-9dbb-9b2b20218538