Oilpan: Build fix after r179181

m_autoTextsizer is gone in r179181. This CL removes the leftover.

TBR=pdr@chromium.org

Review URL: https://codereview.chromium.org/423293003

git-svn-id: svn://svn.chromium.org/blink/trunk@179184 bbb929c8-8fbe-4397-9dbb-9b2b20218538