[Flags] Extension for frozen autofill experiments

These flags are covering inherited UI projects that improve the autofill
experience. By next year, we can probably make a call to deprecate at
least one of them. Until then, they are inactive but still in
consideration.

Bug: None
Change-Id: I551b2b14b41b25ebf7946ecfb1530633e50d5274
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2534854Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Commit-Queue: Friedrich [CET] <fhorschig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826805}

chrome/browser/flag-metadata.json

@@ -373,12 +373,12 @@
   {
     "name": "autofill-use-improved-label-disambiguation",
     "owners": [ "fhorschig" ],
-    "expiry_milestone": 87
+    "expiry_milestone": 90
   },
   {
     "name": "autofill-use-mobile-label-disambiguation",
     "owners": [ "fhorschig" ],
-    "expiry_milestone": 87
+    "expiry_milestone": 90
   },
   {
     "name": "autofill-use-renderer-ids",
@@ -2140,7 +2140,7 @@
   {
     "name": "enable-suggestions-with-substring-match",
     "owners": [ "fhorschig" ],
-    "expiry_milestone": 87
+    "expiry_milestone": 90
   },
   {
     "name": "enable-surface-control",