DevTools: get rid of status bar buttons (panel-specific solution applied).

BUG=307085
R=vsevik@chromium.org

Review URL: https://codereview.chromium.org/26337003

git-svn-id: svn://svn.chromium.org/blink/trunk@159771 bbb929c8-8fbe-4397-9dbb-9b2b20218538