Defer expiry of the pull-to-refresh flag

BUG=1110719

Change-Id: Id09e4e9b336d12acb99ad648e0dd3ad83130185f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425066Reviewed-by: Mohsen Izadi <mohsen@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809678}

chrome/browser/flag-metadata.json

@@ -3770,8 +3770,8 @@
   },
   {
     "name": "pull-to-refresh",
-    "owners": [ "afakhry" ],
-    "expiry_milestone": 83
+    "owners": [ "afakhry", "tclaiborne" ],
+    "expiry_milestone": 89
   },
   {
     "name": "query-tiles",