Add owner and target milestone for the LayoutNG flag

Change-Id: Iec7f382006b6215b6ac1b847722511f66ff82db2
Reviewed-on: https://chromium-review.googlesource.com/c/1344200Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609830}

chrome/browser/flag-metadata.json

@@ -1313,8 +1313,8 @@
   },
   {
     "name": "enable-layout-ng",
-    // "owners": [ "your-team" ],
-    "expiry_milestone": 76
+    "owners": [ "layout-dev@chromium.org" ],
+    "expiry_milestone": 80
   },
   {
     "name": "enable-lazy-frame-loading",