Extend expiry date for sxg related features

Bug: 935267, 968427
Change-Id: I8648d57e4266427705cbd9e2cbfc67ee2728631b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1916535Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715567}

chrome/browser/flag-metadata.json

@@ -1868,12 +1868,12 @@
   {
     "name": "enable-sxg-prefetch-cache-for-navigations",
     "owners": [ "horo", "//content/browser/web_package/OWNERS" ],
-    "expiry_milestone": 80
+    "expiry_milestone": 85
   },
   {
     "name": "enable-sxg-subresource-prefetching",
     "owners": [ "horo", "//content/browser/web_package/OWNERS" ],
-    "expiry_milestone": 80
+    "expiry_milestone": 85
   },
   {
     "name": "enable-sync-device-info-in-transport-mode",