Make /proc/sys/kernel/perf_event_max_sample_rate accessible to untrusted_app.

perf_event_max_sample_rate is needed to be read for native profiling,
otherwise CTS test can fail on devices with kernel >= 4.4. Before this CL,
the file is not readable from untrusted_app domain. This CL makes it readable
from both shell domain and untrusted_app domain.

Bug: http://b/35554543
Test: build and test on marlin.
Change-Id: Id118e06e3c800b70a749ab112e07a4ec24bb5975
diff --git a/private/genfs_contexts b/private/genfs_contexts
index e84b494..7873367 100644
--- a/private/genfs_contexts
+++ b/private/genfs_contexts
@@ -22,6 +22,7 @@
 genfscon proc /sys/kernel/kptr_restrict u:object_r:proc_security:s0
 genfscon proc /sys/kernel/modprobe u:object_r:usermodehelper:s0
 genfscon proc /sys/kernel/modules_disabled u:object_r:proc_security:s0
+genfscon proc /sys/kernel/perf_event_max_sample_rate u:object_r:proc_perf:s0
 genfscon proc /sys/kernel/poweroff_cmd u:object_r:usermodehelper:s0
 genfscon proc /sys/kernel/randomize_va_space u:object_r:proc_security:s0
 genfscon proc /sys/kernel/usermodehelper u:object_r:usermodehelper:s0