Introduce system_file_type

system_file_type is a new attribute used to identify files which exist
on the /system partition. It's useful for allow rules in init, which are
based off of a blacklist of writable files. Additionally, it's useful
for constructing neverallow rules to prevent regressions.

Additionally, add commented out tests which enforce that all files on
the /system partition have the system_file_type attribute. These tests
will be uncommented in a future change after all the device-specific
policies are cleaned up.

Test: Device boots and no obvious problems.
Change-Id: Id9bae6625f042594c8eba74ca712abb09702c1e5
diff --git a/public/cppreopts.te b/public/cppreopts.te
index fb9855e..623391e 100644
--- a/public/cppreopts.te
+++ b/public/cppreopts.te
@@ -5,7 +5,7 @@
 # directories.
 
 type cppreopts, domain, mlstrustedsubject;
-type cppreopts_exec, exec_type, file_type;
+type cppreopts_exec, system_file_type, exec_type, file_type;
 
 # Allow cppreopts copy files into the dalvik-cache
 allow cppreopts dalvikcache_data_file:dir { add_name remove_name search write };