Adding owners to ARC CUPS API chrome flag

Per (https://sites.google.com/a/chromium.org/dev/flag-ownership), we
need to tag our chrome flags with owners.

Bug: N/A
Change-Id: I31b90d6cc736e48edd37982c267ce8d2094b8b42
Tests: Regressions pass
Reviewed-on: https://chromium-review.googlesource.com/c/1344581Reviewed-by: Sean Kau <skau@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Luum Habtemariam <luum@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609804}

chrome/browser/flag-metadata.json

@@ -763,7 +763,7 @@
   },
   {
     "name": "enable-arc-cups-api",
-    // "owners": [ "your-team" ],
+    "owners": [ "luum", "skau" ],
     "expiry_milestone": 76
   },
   {