Extend files-ng feature flag expiry date

Bug: 992818
Change-Id: I45a74425ddbc340526696b4e67fded93be96c5ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2102937
Auto-Submit: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Alex Danilo <adanilo@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Alex Danilo <adanilo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750458}

chrome/browser/flag-metadata.json

@@ -2312,7 +2312,7 @@
   {
     "name": "files-ng",
     "owners": [ "adanilo", "noel" ],
-    "expiry_milestone": 85
+    "expiry_milestone": 86
   },
   {
     "name": "files-unified-media-view",