Rename NavigatorServiceWorkerInterface to ServiceWorkerContainer

Per the latest spec change (thanks to Alec for raising this issue):
https://github.com/slightlyoff/ServiceWorker/commit/5ef8bdd6f7a26beff131d0f04b680de10d29e43c

BUG=285976
TEST=http/tests/serviceworker

Review URL: https://codereview.chromium.org/130693010

git-svn-id: svn://svn.chromium.org/blink/trunk@167021 bbb929c8-8fbe-4397-9dbb-9b2b20218538