flags: update flag ownership doc URL

TBR=avi@chromium.org

Bug: None
Change-Id: Ifbff77761cb69ef2d5f8c765d4aea1df63906459
Reviewed-on: https://chromium-review.googlesource.com/c/1343074Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609681}

chrome/browser/flag-metadata.json

@@ -3,7 +3,7 @@
 // of the review process and to clean up flags that have become obsolete or
 // unused. For more details, see:
 //
-//    https://sites.google.com/a/chromium.org/dev/flag-ownership
+//    https://sites.google.com/a/chromium.org/dev/developers/contributing-code/flag-ownership
 //
 // This file is a list of json objects; each object contains these keys:
 //