base

Fix #2176803 - restores from userdebug to user builds not working

The underlying issue is that ordinarily, the restore mechanism checks the
signature block of the package which uploaded the restore data against the
signature of the package on-device that will be handling the restore.  This is
to ensure that the restore goes to the "same" application as the one that
uploaded it.

However, applications bundled on the system partition as part of the device
build are signed not with a permanent, app-identifying signature, but rather
with the device's signature block, which is different for each kind of device
and potentially between kinds of build for the same device.  That renders the
stored backup data unusable when changing devices / builds / etc.

This change works around the problem by explicitly privileging applications that
reside on the system partition:  they have been built into the device, and so
are trusted to be able to handle data that is marked as coming from its package
name.

Change-Id: I561011bce2b54cff3e695e82e7544b126b6ac31e