Add screencap domain.

Only seeing this denial in permissive:
allow shell screencap_exec:file getattr;

Bug: 37565047
Test: adb shell screencap w/o root
Test: cts-tradefed run cts-dev --module CtsAadbHostTestCases
Merged-In: I9f31d2067e002e7042646ee38dbfc06687481ac7
Change-Id: I9f31d2067e002e7042646ee38dbfc06687481ac7
diff --git a/private/file_contexts b/private/file_contexts
index 0bdb1f7..4029256 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -210,6 +210,7 @@
 /system/bin/mediametrics	u:object_r:mediametrics_exec:s0
 /system/bin/cameraserver	u:object_r:cameraserver_exec:s0
 /system/bin/mediaextractor	u:object_r:mediaextractor_exec:s0
+/system/bin/screencap	u:object_r:screencap_exec:s0
 /system/bin/mdnsd	u:object_r:mdnsd_exec:s0
 /system/bin/installd	u:object_r:installd_exec:s0
 /system/bin/otapreopt_chroot   u:object_r:otapreopt_chroot_exec:s0