Add scheduler-bugs@chromium.org watchlist

This patch adds a watchlist for scheduling related code reviews.

BUG=432040

Review URL: https://codereview.chromium.org/715793002

git-svn-id: svn://svn.chromium.org/blink/trunk@185128 bbb929c8-8fbe-4397-9dbb-9b2b20218538