Unregister with push service and SW database when permission is lost.
This CL makes the PushService a ContentSettings observer and check
for the subscriber's origin permission when a ContentSettings change
might have changed it.
BUG=
443228
Committed:
https://crrev.com/8082d50a6306b1b93619a16836579044c562b98e
Cr-Commit-Position: refs/heads/master@{#316799}