Make all //build OWNERS owners for //BUILD.gn as well.

This gets us more owners for build changes, and makes things a
bit more consistent.

R=thakis@chromium.org
TBR=brettw@chromium.org

Review-Url: https://codereview.chromium.org/2026373002
Cr-Commit-Position: refs/heads/master@{#397287}

OWNERS

@@ -7,9 +7,14 @@ jam@chromium.org
 per-file .gitignore=*
 per-file .git-blame-ignore-revs=mgiuca@chromium.org
 per-file .git-blame-ignore-revs=thakis@chromium.org
-per-file BUILD.gn=dpranke@chromium.org
-per-file DEPS=*
+
 per-file AUTHORS=*
-per-file WATCHLISTS=*
+
+per-file BUILD.gn=file://build/OWNERS
+
+per-file DEPS=*
+
 per-file PRESUBMIT*.py=jochen@chromium.org
 per-file PRESUBMIT*.py=phajdan.jr@chromium.org
+
+per-file WATCHLISTS=*