WebUI Tab Strip: Update flag expiration milestones

Change-Id: I48726f5b7a5128cd3e4c3481a5628b64ee002b24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062641Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742972}

chrome/browser/flag-metadata.json

@@ -3771,13 +3771,13 @@
   },
   {
     "name": "webui-tab-strip",
-    "owners": [ "johntlee", "pbos" ],
-    "expiry_milestone": 82
+    "owners": [ "collinbaker", "johntlee" ],
+    "expiry_milestone": 85
   },
   {
     "name": "webui-tab-strip-demo-options",
     "owners": [ "johntlee", "dpapad" ],
-    "expiry_milestone": 82
+    "expiry_milestone": 85
   },
   {
     "name": "webxr-incubations",