[ios] Add flag ownership for rohitrao

iOS flag owners were asked to claim ownership and state an expiry in
this announcement email:
https://groups.google.com/a/google.com/g/bling-team/c/7YC_3l6yEzo/m/1-iZg1fPAAAJ

This is one of several CLs that adds iOS flag ownership information into
flag-metadata.json.

The owner of these flags was identified via git blame. A placeholder
expiry milestone of M86 was added. Please either LGTM, or suggest a new
owner and/or expiry.

Bug: 1058614
Change-Id: I973334e2bf430038cef630a5034c3a98c20ed19e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2093914Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748302}

chrome/browser/flag-metadata.json

@@ -2258,6 +2258,11 @@
     // RTL UI layout.
     "expiry_milestone": -1
   },
+  {
+    "name": "force-unstacked-tabstrip",
+    "owners": [ "//ios/chrome/browser/ui/tabs/OWNERS" ],
+    "expiry_milestone": 86
+  },
   {
     "name": "force-update-menu-type",
     "owners": [ "//chrome/android/java/src/org/chromium/chrome/browser/omaha/OWNERS" ],