Extend expiry for enable-app-grid-ghost flag

Bug: 1085286
Change-Id: Idc4ca14e4373988461995a6a00713bf6226e9346
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2212757
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Auto-Submit: Matthew Mourgos <mmourgos@chromium.org>
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771241}

chrome/browser/flag-metadata.json

@@ -1122,7 +1122,7 @@
   {
     "name": "enable-app-grid-ghost",
     "owners": [ "mmourgos" ],
-    "expiry_milestone": 82
+    "expiry_milestone": 88
   },
   {
     "name": "enable-app-list-search-autocomplete",