Also make _RietveldOwnerAndReviewers have same semantics as before,
to resolve immediate bug until chromium checkouts of developers are
updated.

BUG=609832
R=machenbach@chromium.org

Review-Url: https://codereview.chromium.org/1955223002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300494 0039d316-1c4b-4281-b951-d872f2087c98