This change adds a dictionary to the returned dictionary of storageManager.estimate() that contains details about usage for each storage backend. The goal is to aid in debugging issues around overuse of specific storage systems.
This change is useful in debugging usage between the various storage systems. Right now, this information is already available to origin's if they manually keep track of the usage delta with each call to a storage API.
Docs: https://github.com/whatwg/storage/issues/63#issuecomment-441857897
Explainers: https://jarryd999.github.io/quota-usage-details/