GitLab

The origin can be determined from the live ServiceWorkerRegistration,
use that instead of requiring the renderer to pass it.

Also, verify that the live registration is active to prevent
BackgroundSyncManager::Register from being called prematurely.

BUG=482012

Review URL: https://codereview.chromium.org/1110993003

Cr-Commit-Position: refs/heads/master@{#327371}