SEPolicy for boringssl_self_test.

This CL adds hand-written SELinux rules to:
 - define the boringssl_self_test security domain
 - label the corresponding files at type boringssl_self_test_marker
   and boringssl_self_test_exec.
 - define an automatic transition from init to boringssl_self_test
   domains, plus appropriate access permissions.

Bug: 137267623
Test: When run together with the other changes from draft CL topic
      http://aosp/q/topic:bug137267623_bsslselftest, check that:
      - both /dev/boringssl/selftest/* marker files are
        present after the device boots.
      - Test: after the boringssl_self_test{32,64} binaries have
        run, no further SELinux denials occur for processes
        trying to write the marker file.

Change-Id: I77de0bccdd8c1e22c354d8ea146e363f4af7e36f
diff --git a/private/file_contexts b/private/file_contexts
index 8e6d00f..32bf827 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -83,6 +83,7 @@
 /dev/block/vold/.+	u:object_r:vold_device:s0
 /dev/block/ram[0-9]*	u:object_r:ram_device:s0
 /dev/block/zram[0-9]*	u:object_r:ram_device:s0
+/dev/boringssl/selftest(/.*)?	u:object_r:boringssl_self_test_marker:s0
 /dev/bus/usb(.*)?       u:object_r:usb_device:s0
 /dev/console		u:object_r:console_device:s0
 /dev/cpu_variant:.*     u:object_r:dev_cpu_variant:s0
@@ -188,6 +189,7 @@
 /system/bin/auditctl	u:object_r:auditctl_exec:s0
 /system/bin/bcc                 u:object_r:rs_exec:s0
 /system/bin/blank_screen	u:object_r:blank_screen_exec:s0
+/system/bin/boringssl_self_test(32|64) u:object_r:boringssl_self_test_exec:s0
 /system/bin/charger		u:object_r:charger_exec:s0
 /system/bin/e2fsdroid		u:object_r:e2fs_exec:s0
 /system/bin/mke2fs		u:object_r:e2fs_exec:s0