This change amends the doRestore() / onRestore() interface to backup agents to
provide the integer android:versionCode of the app that stored the backup set.
This should help agents figure out how to handle whatever historical data set
they're handed at restore time.
In addition to the signatures of each participating application, we now also
store the versionCode of each backed-up package, plus the OS version running on
the device that contributed the backup set. We also refuse to process a backup
from a later OS revision to an earlier one, or from a later app version to an
earlier.
LocalTransport has been modified as well to be more resilient to changes in the
system's use of metadata pseudopackages.
We now record the version number of the app (drawn from its manifest versionCode
attribute) along with its signatures. At restore time, we compare the version
associated with the restore set with the version present on the device. If the
restore set is from a newer version of the app than is present on device, we do
not perform the restore operation.
Also fix the pending-backup iteration in 'dumpsys backup'.
Under a pseudo-app for the Package Manager, we store the app signatures for all
participating applications installed on the device. At restore time we will
restore this first, then ensure that the current on-device signature chain is
compatible with the one in the backup set. If there's a mismatch, this may be a
spoof attempt and we will refuse to restore that app's data.
The restore side of this is not implemented, but the Package Manager agent is
here as well as the backup side theoretically pushing the data now.
