1. Updated the security mode of the print spooler. Now the spooler
is not signed with the system key, it is not a privileged app so if
it gets compromised (PDF rendering is a potential attack vector)
it cannot access dangerous permissions. Also only the system
can bind to the spooler.
2. Added APIs for asking a print service to start and stop tracking
a given printer. This is need for the case when the user selects
the printer and the print service should do a best effort to keep
the system updated for the current state of the printer.
3. Added APIs for putting a print job in a blocked state. A print
service would report the print job as blocked if for some reason
the printer cannot proceed, e.g. 99 pages are printed but there
is no paper for the last one. The user has to add more paper
and the print service can resume the job.
4. Changed the read/write APIs to use ParcelFileDescriptor instead
of FileDescriptor since the latter does not have a clean API for
detaching the wrapped Linux file descriptor when one wants to
push it to native.
5. Added API for getting the size of the printed document so the
print service can avoid handling big filed over cellular network
or ask the user if needed.
6. Now the print services that are preinstalled on the system image
are automatically enabled.
Change-Id: Ia06c311d3d21cabb9e1368f13928e11cd0030918
d26d4898fc