Service Worker: Add ServiceWorkerContainer.getRegistrations() method.

Implement ServiceWorkerContainer.getReistrations() method as per spec:
https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#navigator-service-worker-getRegistrations

In this patch, ServiceWorkerDatabase::GetRegistrationsForOrigin() has been
changed to additionally retrieving resources so a newly added
ServiceWorkerStorage::DiDGetRegistrations() can get all the stored real
registrations by calling ServiceWorkerStorage::GetOrCreateRegistration().
ServiceWorkerStorage::DidGetRegistrationsInfos() remained as-is used by
ServiceWorkerStorage::GetAllRegistrationsInfos() to get a vector of
ServiceWorkerRegistrationInfo objects.

Companion CL (Blink): https://codereview.chromium.org/1165363003/
Companion CL (Blink layout tests): https://codereview.chromium.org/1168393002/

BUG=478382

Review URL: https://codereview.chromium.org/1146913004

Cr-Commit-Position: refs/heads/master@{#333886}
20 files changed