Mark standalone/io/file_system_watcher_test flaky on mac

tests/standalone/standalone.status

Index: tests/standalone/standalone.status
===================================================================
--- tests/standalone/standalone.status	(revision 27171)
+++ tests/standalone/standalone.status	(working copy)
@@ -18,6 +18,7 @@
 [ $runtime == vm ]
 package/package_isolate_test: Fail # http://dartbug.com/7520.
 
+
 [ $runtime == vm && $checked ]
 # These tests have type errors on purpose.
 io/process_invalid_arguments_test: Fail, OK
@@ -35,6 +36,7 @@
 # This is expected as MacOS by default runs with a very low number
 # of allowed open files ('ulimit -n' says something like 256).
 io/socket_many_connections_test: Skip
+io/file_system_watcher_test: Pass, Timeout # Issue 13065
 
 # These tests pass on MacOS 10.8.2 but fails on the buildbot machines
 # that are running an earlier version of MacOS. The issue is that the