Before screencap was in its own domain, it was able to do
this by using all of shell's permissions.

The following denials are caused (along with times from running the below test command)
when screencap is invoked to write a file onto the sdcard:
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:23): avc: denied { read } for name="primary" dev="tmpfs" ino=19547 scontext=u:r:screencap:s0 tcontext=u:object_r:storage_file:s0 tclass=lnk_file permissive=1
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:24): avc: denied { search } for name="/" dev="tmpfs" ino=19529 scontext=u:r:screencap:s0 tcontext=u:object_r:tmpfs:s0 tclass=dir permissive=1
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:25): avc: denied { search } for name="user" dev="tmpfs" ino=19535 scontext=u:r:screencap:s0 tcontext=u:object_r:mnt_user_file:s0 tclass=dir permissive=1
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:26): avc: denied { read } for name="primary" dev="tmpfs" ino=31198 scontext=u:r:screencap:s0 tcontext=u:object_r:mnt_user_file:s0 tclass=lnk_file permissive=1
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:27): avc: denied { search } for name="/" dev="sdcardfs" ino=1310722 scontext=u:r:screencap:s0 tcontext=u:object_r:sdcardfs:s0 tclass=dir permissive=1
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:28): avc: denied { write } for name="image.png" dev="sdcardfs" ino=1310764 scontext=u:r:screencap:s0 tcontext=u:object_r:sdcardfs:s0 tclass=file permissive=1
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:29): avc: denied { open } for path="/storage/emulated/0/image.png" dev="sdcardfs" ino=1310764 scontext=u:r:screencap:s0 tcontext=u:object_r:sdcardfs:s0 tclass=file permissive=1
08-30 21:03:32.009  4986  4986 I screencap: type=1400 audit(0.0:30): avc: denied { write open } for path="/data/media/0/image.png" dev="sda45" ino=1310764 scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file permissive=1
08-30 21:03:32.582  4990  4990 I screencap: type=1400 audit(0.0:31): avc: denied { execute } for name="sh" dev="dm-0" ino=998 scontext=u:r:screencap:s0 tcontext=u:object_r:shell_exec:s0 tclass=file permissive=1
08-30 21:03:32.582  4990  4990 I screencap: type=1400 audit(0.0:32): avc: denied { read open } for path="/system/bin/sh" dev="dm-0" ino=998 scontext=u:r:screencap:s0 tcontext=u:object_r:shell_exec:s0 tclass=file permissive=1
08-30 21:03:32.582  4990  4990 I screencap: type=1400 audit(0.0:33): avc: denied { execute_no_trans } for path="/system/bin/sh" dev="dm-0" ino=998 scontext=u:r:screencap:s0 tcontext=u:object_r:shell_exec:s0 tclass=file permissive=1
08-30 21:03:32.582  4990  4990 I sh      : type=1400 audit(0.0:34): avc: denied { getattr } for path="/system/bin/sh" dev="dm-0" ino=998 scontext=u:r:screencap:s0 tcontext=u:object_r:shell_exec:s0 tclass=file permissive=1
08-30 21:03:32.586  4990  4990 I sh      : type=1400 audit(0.0:35): avc: denied { ioctl } for path="socket:[57515]" dev="sockfs" ino=57515 ioctlcmd=5401 scontext=u:r:screencap:s0 tcontext=u:r:adbd:s0 tclass=unix_stream_socket permissive=1
08-30 21:03:32.586  4990  4990 I sh      : type=1400 audit(0.0:36): avc: denied { getattr } for path="socket:[57515]" dev="sockfs" ino=57515 scontext=u:r:screencap:s0 tcontext=u:r:adbd:s0 tclass=unix_stream_socket permissive=1
08-30 21:03:32.589  4991  4991 I sh      : type=1400 audit(0.0:37): avc: denied { execute_no_trans } for path="/system/bin/am" dev="dm-0" ino=1178 scontext=u:r:screencap:s0 tcontext=u:object_r:system_file:s0 tclass=file permissive=1
08-30 21:03:32.739  4992  4992 I cmd     : type=1400 audit(0.0:38): avc: denied { call } for scontext=u:r:screencap:s0 tcontext=u:r:system_server:s0 tclass=binder permissive=1
08-30 21:03:32.739  4992  4992 I cmd     : type=1400 audit(0.0:39): avc: denied { use } for path="/dev/null" dev="tmpfs" ino=19514 scontext=u:r:system_server:s0 tcontext=u:r:screencap:s0 tclass=fd permissive=1
08-30 21:03:32.739  4992  4992 I cmd     : type=1400 audit(0.0:40): avc: denied { transfer } for scontext=u:r:screencap:s0 tcontext=u:r:system_server:s0 tclass=binder permissive=1
08-30 21:03:32.741   575   575 E SELinux : avc:  denied  { find } for service=activity pid=4992 uid=2000 scontext=u:r:screencap:s0 tcontext=u:object_r:activity_service:s0 tclass=service_manager permissive=1
08-30 21:03:32.749   837   837 I Binder:837_9: type=1400 audit(0.0:41): avc: denied { call } for scontext=u:r:system_server:s0 tcontext=u:r:screencap:s0 tclass=binder permissive=1

If /data/media/ is deleted, the following denials also occur:
08-31 00:45:45.966  8899  8899 I screencap: type=1400 audit(0.0:43): avc: denied { search } for name="0" dev="sda45" ino=1310728 scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=dir permissive=1
08-31 00:45:45.966  8899  8899 I screencap: type=1400 audit(0.0:44): avc: denied { read open } for path="/data/media/0" dev="sda45" ino=1310728 scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=dir permissive=1
08-31 00:45:45.966  8899  8899 I screencap: type=1400 audit(0.0:48): avc: denied { write } for name="0" dev="sda45" ino=1310728 scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=dir permissive=1
08-31 00:45:45.966  8899  8899 I screencap: type=1400 audit(0.0:49): avc: denied { add_name } for name="image.png" scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=dir permissive=1
08-31 00:45:45.966  8899  8899 I screencap: type=1400 audit(0.0:50): avc: denied { create } for name="image.png" scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file permissive=1
08-31 00:45:45.966  8899  8899 I screencap: type=1400 audit(0.0:51): avc: denied { setattr } for name="image.png" dev="sda45" ino=1310764 scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file permissive=1
08-31 00:45:45.966  8899  8899 I screencap: type=1400 audit(0.0:53): avc: denied { write open } for path="/data/media/0/image.png" dev="sda45" ino=1310764 scontext=u:r:screencap:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file permissive=1
08-31 01:04:29.741  6625  6625 W screencap: type=1400 audit(0.0:23): avc: denied { write } for name="0" dev="sdcardfs" ino=655364 scontext=u:r:screencap:s0 tcontext=u:object_r:sdcardfs:s0 tclass=dir permissive=0

Test: adb shell screencap -p /sdcard/phone.png
Bug: 65206688
Change-Id: I808429b25fa3118fef7931050ab757c9bcd61881