flags: assign extension-content-verification to extensions OWNERS

Bug: None
Change-Id: I9893f16efc9a61fb8c75c606a593fcff8bb1c537
Reviewed-on: https://chromium-review.googlesource.com/c/1434800
Auto-Submit: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625792}

chrome/browser/flag-metadata.json

@@ -2245,7 +2245,7 @@
   },
   {
     "name": "extension-content-verification",
-    // "owners": [ "your-team" ],
+    "owners": [ "//extensions/OWNERS" ],
     "expiry_milestone": 76
   },
   {