Make platform_FilePerms non-Experimental.

Has been passing with no flake on any platform for more than 10 build:

https://wmatrix.googleplex.com/unfiltered?hide_missing=True&releases=tot&tests=platform_FilePerms

BUG=chromium:335617
TEST=Passes on daisy_spring, passes on the bots.

Change-Id: I6dcbfc5257b2f53f83373bca2806edc02be3c74a
Reviewed-on: https://chromium-review.googlesource.com/184559
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
diff --git a/client/site_tests/platform_FilePerms/control b/client/site_tests/platform_FilePerms/control
index ea89f92..5750cbf 100644
--- a/client/site_tests/platform_FilePerms/control
+++ b/client/site_tests/platform_FilePerms/control
@@ -14,7 +14,6 @@
 TEST_CATEGORY = "Functional"
 TEST_CLASS = "platform"
 TEST_TYPE = "client"
-EXPERIMENTAL = "True"
 
 DOC = "Verifies permissions on various file systems."