Any package can now participate in backup/restore, without requiring any
manifest-declared permission. *Control* of the backup manager is still
guarded by the BACKUP permission, which is signatureOrSystem.
Change-Id: I116fcfcd4cd255e3c976330da1c4dea7d4faae9d
Packages that do not use android.permission.BACKUP_DATA will neither be backed
up nor restored. That permission is currently signature-only. In the future if
access to the backup/restore infrastructure is made available to arbitrary 3rd
party applications, the permission checks (and indeed, the permission itself)
can simply be removed.
Backups will be handled by launching the application in a special
mode under which no activities or services will be started, only
the BackupAgent subclass named in the app's android:backupAgent
manifest property. This takes the place of the BackupService class
used earlier during development.
In the cases of *full* backup or restore, an application that does
not supply its own BackupAgent will be launched in a restricted
manner; in particular, it will be using the default Application
class rather than any manifest-declared one. This ensures that the
app is not running any code that may try to manipulate its data
while the backup system reads/writes its data set.
