DevTools: revert r155534 for breaking console auto-scroll.

BUG=275581
R=vsevik@chromium.org

Review URL: https://codereview.chromium.org/22986011

git-svn-id: svn://svn.chromium.org/blink/trunk@156394 bbb929c8-8fbe-4397-9dbb-9b2b20218538