Extend shared highlights flag expiry

Bug: None
Change-Id: Ia92791c401c483d2dff98ca3583f087baa9e4bcc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2543691
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Auto-Submit: Gayane Petrosyan <gayane@chromium.org>
Reviewed-by: Sebastien Lalancette <seblalancette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828264}

chrome/browser/flag-metadata.json

@@ -479,7 +479,7 @@
   {
     "name": "chrome-share-highlights-android",
     "owners": [ "gayane" ],
-    "expiry_milestone": 88
+    "expiry_milestone": 90
   },
   {
     "name": "chrome-share-long-screenshot",