Datastores are preloaded only for content principals. The preloading is triggered as soon as possible to lower the chance of blocking the main thread in content process. If there is no physical database on disk for given origin, datastore is not created. Preloaded datastores are kept alive for 20 seconds.
An attribute for checking if the next gen local storage implementation is enabled is exposed via a new interface nsILocalStorageManager which should be used for any other local storage specific stuff.
The implementation is based on a cache (datastore) living in the parent process and sync IPC calls initiated from content processes.
IPC communication is done using per principal/origin database actors which connect to the datastore.
The synchronous blocking of the main thread is done by creating a nested event target and spinning the event loop.
