Add davidben to prerender OWNERs.

R=cbentzel@chromium.org

Review URL: https://codereview.chromium.org/117453003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241591 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241591