Allow compos_fd_server to signal readiness

We pass the write end of a pipe to fd_server which it uses to signal
when it is ready to serve.

Bug: 201764092
Test: atest ComposTestCase
Change-Id: Id952e953e79f6cef9c8f0c847a303a3a854f2248
diff --git a/private/compos_fd_server.te b/private/compos_fd_server.te
index 16a57e2..5b11f26 100644
--- a/private/compos_fd_server.te
+++ b/private/compos_fd_server.te
@@ -5,6 +5,9 @@
 allow compos_fd_server odrefresh:fd use;
 allow compos_fd_server apex_art_data_file:file { getattr read };
 allow compos_fd_server apex_art_staging_data_file:file { getattr read write };
+# Use a pipe to signal readiness
+allow compos_fd_server odrefresh:fifo_file write;
+
 # TODO(b/196109647) - remove this when no longer needed by minijail
 allow compos_fd_server odrefresh:fifo_file read;