Extend enable-custom-mac-paper-sizes flag.

Still slowly working through the launch. Also add another owner.

Bug: 477699
Change-Id: I3c6dd7e7f0236a0e803a23c32e6716c493bd3c7c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2066278
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743231}

chrome/browser/flag-metadata.json

@@ -1224,8 +1224,8 @@
   },
   {
     "name": "enable-custom-mac-paper-sizes",
-    "owners": [ "thestig" ],
-    "expiry_milestone": 82
+    "owners": [ "thestig", "dhoss" ],
+    "expiry_milestone": 85
   },
   {
     "name": "enable-data-reduction-proxy-server-experiment",